Mtn
Billed for handset after contrect expired

My MTN contract ran from 6 Jan 2011 to 6 Jan 2013 and has now gone onto a month to month basis.
The contract is a 'Top Up 100' package which included a handset which totalled R250.
The contract is no over yet I am still been billed R250 but should only be billed thr - R100 for a 'Top Up 100'.
I called 808 was informed I need to fill in migration documentation.
Why has the contract not automatically been adjusted to the correct amount now that the 2 year term is over and why do I need to fill in migration documentation when the contract should still stay a 'Top Up 100' but the only difference is now it is on a month to month basis. I was billed extra on the 21 Jan 2013 and 21 Feb 2013 for the handset.
Please can this be looked at and my account corrected.

Company: Mtn
Country: South Africa
City: Contract

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