My account was handed over to MBD debt collectors it was settled

My account was handed over to MBD debt collectors it was settled last year late, my account is still in active and MBD keeps calling me and sending me messages that the account is still out standing even after calling the customer service department and the advised that the account is not owed and i was told there is nothing they can do about it other than giving me a letter to show that the account is paid up.