MTN REAP OFF PEOPLE

Took a data contract with MTN 3 years ago when the period ended they put me on Month to month contract without communicating or warning me like other service providers,I went to their stores on Mall of Tembisa to query why my instalment was flactuating,I was told tht my router is old and tht there are no new deals they can offer me,

I blocked them from deducting money but now the installment keeps on accumulating, they dont want to cancel the contract they say I must pay what is due to them