UNRESOLVED BILLED STATEMENT WITH WRONG CELL NUMBER

have been battling with MTN since Nashua moved my account to MTN in December 2014.I'm convinced that their credit department is not in order. my services were suspended in March claiming that I owe them the December 2014 and yes, it was discovered that the payment was made into Nashua's account .Nashua paid back on March 20th and I paid the money into MTN's account on the 23 March and made my monthly payment again on the 30th March but now when I wish to upgrade as contract is long overdue in August ,I'm told that I have 90 days arrears and I asked MTN if so for which month exactly &amp