Product: Debt collection

In 2017, I arrived in the US through the Cuban Medical Permit Program ( CMPP ) ; XXXX XXXX received me, and with help from the government for 3 months, I settled with my son in an apartment in the XXXX  at XXXX XXXX located at XXXX XXXX  XXXX XXXX XXXX XXXX, TX, XXXX, after that I should be able to support myself, to me and my son. Since at that time I still did not have social security, the rental contract was made by XXXX XXXX in my name. The conditions of that condominium were terrible, I spent 4 months from XXXX to XXXX with extreme temperatures in XXXX without air conditioning despite multiple emergency reports and of which I requested evidence from the office ( attached ), wastewater flooding in the kitchen coming from the XXXX floor, cockroaches, extreme insecurity ... reasons for which I could terminate the contract as established in article XXXX ( attached ) and I did not do so because I did not want to damage my credit. In the last days of XXXX I went to the office to communicate that my contract would end on XX/XX/XXXX and that I would not renew it, so from that day the apartment would already be vacant. At that moment they gave me a piece of paper and a pen so that I could notify it by written and they filed. 
On Sunday XX/XX/2017 I moved into XXXX XXXX at XXXX XXXX XXXX, XXXX, TX, XXXX ( evidence of contract attached ) ; and on XX/XX/XXXX ( last day of the contract at XXXX  at XXXX XXXX ) I went to deliver the key because the office was closed on the Sunday of the move. The person who picked up the key told me that I had to pay the rent for the next month ( XXXX ) " because of me they couldn't rent the apartment for that month. '' Despite the notice I gave a month in advance, of them having service keys to the apartment, of the days of maintenance necessary before renting the apartment again, and of me still being on the last day of my contract. I thought that this person was wrong and did not know the term of my contract and I told her that I did not owe anything because everything was in order, and she replied to my face : " you have to pay, and if you don't I will send you to an agency of collection ''. 
I still thought that when I left the office she would rectify the information and forget the fact. A few months later I get a call from RENTRECOVERYSOLUTIONS, asking me to give them my social security number because I had a debt with the XXXX  at XXXX XXXX that they had to collect ; I told them that there was a mistake and that I had no debt, they insisted several times that I give them my social security number, trying to confirm my identity with a false email that was unknown to me ; I repeated that they were in error and dismissed the call. 
6 years later, 2 days ago I received notification from XXXX that I have a debt in Collection of XXXX XXXX for this reason, obviously damaging my credit with all that it entails. 
Telling very briefly about myself, in the 6 years that I have been in the US I became a citizen, studied and graduated from a university degree, bought my own house, I have always had an excellent XXXX XXXX and an exceptional payment history in all my accounts ( attached the credit report ). Last year I was diagnosed with XXXX XXXX, I had multiple exams, XXXX major surgeries, therapies and I am still undergoing treatment which increased the use of XXXX of my cards, and despite that I work honestly without asking for any help from the government and I maintain all my payments on time.