Citibank Bank Account Or Service Complaint

Citibank Bank account or service department,

Checking account Making/receiving payments, sending money California

In - of this year I received a collection letter from - stating they are collecting on behalf of CITI bank for the account in default. I NEVER HAD citi bank account!!! I disputed this with - bureaus and with - who failed to validate this account and send me any proof that I was the debtor on this account but advised me to get a letter from CITI bank stating that I never had an account with them. I called - # for citi bank, who advised me to inquire with the branch for the letter. But branch manager advised me to call their fraud department who directed me to the local branch again .... I also have written several request to citi bank asking them to validate this account but all went ignored. I am not stuck with the collection that does NOT belong to me and with collection company - who is ILLEGALLY attempting to collect debt and harassing me non stop!