Question: Which Belgium telecommunications operator was previously owned a telecommunications company based in The Hague?

Context paragraphs:
Eir (telecommunications): Eircom Limited, trading as eir, is a fixed, mobile and broadband telecommunications company in Ireland, and a former state-owned monopolist.  It is the largest telecommunications operator in the Republic, with a division to service the business and corporate telecom markets in Northern Ireland and Britain.  As Bord Telecom Éireann, the company was state-owned until 1999, when it was floated on the Irish and New York Stock Exchanges.

Base (mobile telephony provider): BASE is the third largest of Belgium's three mobile telecommunications operators.  It is a subsidiary of Telenet.  It competes with Proximus and Orange Belgium.  It was previously owned by KPN and sold to Telenet in 2015.

Telekom Srpske: Telekom Srpske (full legal name: Telekom Srpske a.d. ) is a telecommunications company based in Banja Luka, Republika Srpska, Bosnia and Herzegovina.  The company is owned by Telekom Srbija, and is the second largest telecommunications company in Bosnia and Herzegovina and the biggest one listed on the Banja Luka Stock Exchange, with the market capitalisation of about €540m.

AT&amp;T: AT&T Inc. is an American multinational telecommunications conglomerate, headquartered at Whitacre Tower in downtown Dallas, Texas.  AT&T is the world's largest telecommunications company.  AT&T is the second largest provider of mobile telephone services and the largest provider of fixed telephone services in the United States, and also provides broadband subscription television services through DirecTV; combined with AT&T's legacy U-verse service, this also makes AT&T the largest pay television operator.  AT&T is the second-largest company in Texas, behind ExxonMobil.  s of February 2017 , AT&T is the 12th largest company in the world (non-oil and overall) as measured by a composite of revenues, profits, assets and market valuation.  AT&T is the largest telecommunications company in the world by revenue.  s of 2017 , it is also the 18th-largest mobile telecom operator in the world, with 134 million mobile customers.  AT&T was ranked at #4 on the 2017 rankings of the world's most valuable brands published by Brand Finance.

Crnogorski Telekom: Crnogorski Telekom is the leading telecommunications operator based in Podgorica, Montenegro.  It is the largest telecommunications company in Montenegro and provides a full range of fixed-line, mobile, IPTV, and internet telecommunication services.

Etisalat (Sri Lanka): Etisalat (Sinhalese: එටිසලාට්; Tamil: எடிசலாட்), is a mobile telecommunications network in Sri Lanka.  It is currently owned by the UAE based telecommunications operator Etisalat.  Etisalat had over 4.2 million customers at the end of February 2012.  The company announced the commercial launch of Dual Carrier HSPA+ services on 15 August 2012, becoming the first operator in South Asia to do so.

KPN: KPN (in full Koninklijke KPN N.V., also Royal KPN N.V.) is a Dutch landline and mobile telecommunications company.  KPN started as a public telecommunications company and is based in The Hague, Netherlands.

Telephone company: A telephone company, also known as a telco, telephone service provider, or telecommunications operator, is a kind of communications service provider (CSP) (more precisely a telecommunications service provider or TSP) that provides telecommunications services such as telephony and data communications access.  Many telephone companies were at one time government agencies or privately owned but state-regulated monopolies.  The government agencies are often referred to, primarily in Europe, as PTTs (postal, telegraph and telephone services).

Telkomtelstra: telkomtelstra is a telecommunications company based in Jakarta, Indonesia.  It was formed as a joint venture between Telkom Indonesia, the nation’s largest fixed-line operator, and Australian telecommunications company, Telstra.  Telkomtelstra offers managed network services, WAN optimisation, managed cloud services, software as a service, infrastructure as a service, platform as a service, unified communication and collaboration services, managed security services, and professional services.  The joint venture was formed in October 2014, and has over 100 employees.

Nexcom Bulgaria: Nexcom Bulgaria, LLC is a licensed telecommunications operator, founded in 1998.  The company is 100% owned by the US Nexcom Telecommunications, LLC, one of the first operators in the world, developing the Voice over Internet protocol technology (VoIP).  Nexcom is the first operator in Bulgaria, providing products and services, based on the VoIP technology.  Prior to selling its wholesale operations in 2003, Nexcom was the leading alternative telecommunications provider in 12 countries throughout Central and Eastern Europe.  Nexcom designed, developed and operated the first pan-regional facilities based VoIP provider in the world.  The company developed a seamless retail and corporate internet telephony solution more than five years before the launch of Skype.

Supporting paragraphs: Base (mobile telephony provider) KPN
Answer: BASE