LINE SWITCHED FROM TOP UP TO OPEN LINE

I have been a loyal customer of MTN for the past 10 years and have not had any issues. However ever since the strike my contract was switched from a top up to an open line without my knowledge!!!!! My monthly amount payable has been R399 for the past year however during the month of March my account came to R2500!!! This is absolutely ridiculous and I refuse to pay the amount. I paid my usual monthly amount however this has noe accumulated and the debit order for this month is R4000!!!! I absolutely refuse to pay this some someone needs to sort this out or I will choose to take legal action against MTN. I had also requested for my debit order date to be changed and this has not been done!!!!!<br> <br> ABSOLUTELY RIDICULOUS SERVICE FROM MTN!!!