Mtn
Account is cancelled but i am still being billed

My contract expired in December 2012 I gave notice and was assured that my contract was cancelled and was then migrated to pre paid.

Today i Received an SMS stating that i owe R289-40.

How can this be my contract is cancelled and where do you get this amount from, the monthly instalments have always been R219-00

Please rectify this immediately as this is totally unacceptable.