Product: Debt collection

I've received numerous harassing & threatening phone calls to collect on a {$14000.00} XXXX credit card debt with a default date of XXXX/XXXXXXXX,  that has passed the NY State statute of limitations, which I understand is 6 years from date of default for this type of debt. XXXX sold the debt to Portfolio Recovery Associates LLC in XXXX. I also receive letters periodically from Portfolio with offers to settle the debt, acknowledging the debt has passed the statute for collection. I've made no payments on the debt since default ; have made no agreements with anyone to pay it. Calls come from all over the country ; I can't identify their true source & they don't appear to be affiliated with Portfolio. I've received no notice that Portfolio has sold the debt to another agency. On XX/XX/XXXX, I sent a certified/return receipt letter to Portfolio asking them to cease & desist, using one  of your sample letters as a guide. I blocked all incoming calls that came from robot or unidentified sources. Phone calls & letters ceased until I got a call from " XXXX XXXX '' ( a process server? ) on XX/XX/XXXX saying a sealed document ( a summons? ) was being delivered to me at my home address the next day, to follow-up with my County Court about it, & if I had any questions to call " XXXX XXXX '' at phone # provided with a case file #. I have no idea who XXXX XXXX is and was immediately suspicious when I called them. They did not identify their company when answering my call, I had to question who they were, what this was all about. I spoke to " XXXX XXXX '' who said they were collecting on the XXXX debt. He said since I hadn't signed any papers yet ( don't know what papers he was talking about ) and hadn't yet received a summons, that was good, & he offered me the opportunity to settle the debt, which I declined to do. I reiterated to him what was stated in my certified letter to Portfolio. XXXX XXXX claimed his records show I made a payment on the account in XXXX, which is patently false. I suffered a catastrophic financial crisis & defaulted on ALL of my credit card accounts at the same time in XX/XX/XXXX. I made absolutely no payments or agreements of any kind on ANY of these defaulted accounts, all of which were charged off by the creditors as bad debts with this one exception of XXXX or Portfolio. I immediately terminated the call with XXXX XXXX. No summons was served on XX/XX/XXXX as XXXX XXXX warned it would be. Prior to this I was also receiving similar calls from an unknown entity " XXXX XXXX '' in NJ, threatening me with the same court action, calling it a " complaint '', not a " debt collection '' matter. That's what prompted me to send the certified letter to Portfolio in XXXX of this year. I think this whole thing is a scam or bluff to get me to make a payment or repayment agreement & re-start the clock on the statute of limitations. This harassment is getting very serious now with me worrying about having to go to court or missing some deadline to answer in court, violating my rights to due process on this expired debt collection. I don't believe any of these unknown callers have standing to collect on the debt since they aren't Portfolio. This all seems illegal to me. HELP!