Neglecting to do their work

I went into a shop to cancel two contracts and upgrade a third.

The upgrade was done without delay (more money) but two and a half months later and they are still billing me for the two contracts that I cancelled.

Needless to say I refused to pay those two contracts now they cut my phone line because of no pay.

I have now made a number off phone calls to get this resolved with no joy. When I phone the call center they keep putting me on hold and then nobody answers the phone again. Longest time on hold was over 20 minutes. When I phone the shop where I cancelled the contracts. They tell me they will come back to me. I am now without a phone. I need someone to resolve this issue urgently.