Shoddy business practices

I signed up for three data packages with Afrihost last year. For the first few months it worked well, but thereafter the service deteriorated on an almost daily basis. I spent countless hours on the phone with them and logged various service queries and every time it would work ok for a few days, but then service went down again. They also increased their prices (with notice - granted), but then expected you to pay an additional R99 per package to keep your double data. I finally tried to cancel on the 25th of January, but the system didn't allow me to do so. I resorted to stopping my debit order as I didn't want to be signed up with them for another month, yet they continued to log reports as if I was connected to them even though my APN had been switched to another user. What they have now resorted to doing, is to block my simcard from being able to use another provider until I pay for data for a full month (even though I wouldn't be able to use said data) which I think is totally wrong of them as they're now preventing me from using my current paid for data - it would seem that they can't stand it if you go to the competition so they resort to lowdown tactics.