R120 H/W Fees increase on contract!!!!

I have been billed R395.00 per month on my MTN contract since September 2013 when I took out the contract with Nashua Mobile. This month however I have received a bill of R548.16 on a cellphone line that I do not even actively use (I blocked the sim card and number after the phone was ****** in Nov 2014). When I compared this bill to my previous bills there has been an increase of R118.46 on H/W Fees alone, which, I assume to be Hardware fees. This means that this is for the handset that was originally included in the contract. How can there be a monthly increase of R118 on a handset on a contract that only has 3 months left to run? There is also a R10 increase in subscription fees that I have not been informed about, nor given permission to be deducted from my bank account. I have tried continuously to contact MTN customer care centre with no success. There has been a total increase of R158.17 from June to July without any explanation and the debit order will be going of on month end. How can they do this?