Cant Cancel Contract for Service not Received

After almost 6 months of cases and calls, Telkom and its service providors were unable to deliver the Unlimited LTE service as promised. The service worked great for the first couple months, but got slower and slower as time passed on. Case numbers ( ********** 4, ********** 1 etc). Now at the end of the contract, cancellation is a pain. Ended up paying for a different service in the mean time, because the Telkom service was nowhere near what was promised. Would like immediate cancellation and credit for the last 6 months of service not received - think its only fair...