Debt collection: Cont'd attempts collect debt not owed

I was contacted by XXXX XXXX from XXXX XXXX, XXXX on XXXX/XXXX/XXXX demanding I pay a debt. I asked what debt? He replied an old XXXX debt. I told him I never had a XXXX account and demanded he send me validation. I received a letter from him dated XXXX/XXXX/XXXX stating I agreed to pay the debt on XXXX/XXXX/XXXX. I sent a response letter to him denying that the debt in question was mine and to send verification. I received a letter from XXXX XXXX XXXX dated XXXX/XXXX/XXXX stating they had received my dispute claiming unauthorized use of account. Today XXXX/XXXX/XXXX I receive XXXX letters from Jefferson Capital.1st dated XXXX/XXXX/XXXX stating they have received my dispute and are unable to resolve and request my SSN, Act #, description of error, dollar amount, date of suspected error, and copy of credit report. It 's been 4 months for them to respond! And then they are asking me for information that I was attempting to get from them for validation! The second letter I received the same day " introducing '' themselves as a debt collector and stating I have 30 days to dispute the debt. Is n't that what I 've been doing since the first phone call and letter four months ago?!