Change in Subs fee 7 months into contract

I have been with MTN for about 15 years now and have had enough of being messed around! In December 2014 I signed a 24 month renewal of my contract for R270 per month. In June 2015 I get billed R290. Now when I take it up with MTN as an error on my account, I get told that MTN has increased the fees in June. This has never been communicated to me. I also signed a 24th contract for R270 and this is the amount I have agreed to for the 24 month period, not anything else. To make things worse, I have paid the R270 from June to now and MTN have suspended my account because of the R20 \shortfall"that I have not paid. <br> <br> I have paid every month the R270 which is what I have agreed to"