Complaint Review: First national collection bureau inc

 I received a letter in the mail saying that I have a delinquent account assigned to their office for collection by their client butterflies holdings. A company that I have never heard of. Unless I notify their office within 30 days they will assume it is valid. I can dispute this debit and this office will obtain verification of the debut or obtain a copy of a judgement and mail it to me. They also said that they could set up an account on a monthly payment plan and they can extend the following discount offer of %50 discount of $2,348.19 payable in 6 payments totaling $1,174.10 each month, I can also pay via check or credit card. Now I think I would remember if I owed anybody $2,348.19 to hsbc bank. I never banked there or had a credit card from this bank so I know this is a scam to collect money from me. They have some made up account number 5458001681204180 and a ref# 124942529. I even checked my credit report and at no time was this on my credit report. If I owed this amount of money it would be there. What can I do to stop this harassment and scam?