Synchrony Financial Debt Collection Complaint

Synchrony Financial Debt collection department,

Credit card Cont'd attempts collect debt not owed Debt was paid North Carolina

My account was sent to - by Synchrony Bank. When the collection agency contacted me I requested for an settlement. After settlement was paid in full - sent back to Synchrony Bank my information stating that the account was paid in full. Synchrony Bank representative stated " they do not show any agreement, although my account started at -, I sill owed - ''. I sent them a copy of the letter that I have from -, stating that my account was paid in full, but I cant get a response from Synchrony Bank.