It is not Wirth it to use mtn as a service provider

We signed a contract with mtn for a 10mb line after we checked covarage. Witch was wery good. For the first 5months of the contract we received the 10mb line we are paying for. Since January we are getting 0.7mb per second witch we can't do nothing with so now we are paying for nothing. We can't cancel the contract without cancelation fees. I have phoned several times. I have send emails to head office as well as customer care, nobody coming back to as to why we are not receiving what we are paying for. This is unacceptable... I need someone to tell me what I can do.

I want to cancel this contract without any cancelation fee or any penalty in writing.