Breach of Contract - Wifi

I have my wifi for almost 2 years now and it has been giving me endless problems. I had signed a contract for a 4mbs line and when it was up an running we were only getting 0.2mbs. We have called several times, sent emails and had technicians sent out to us and almost 2 years down the line nothing has still been done to fix my problem. On the last visit, the technician advised that we need to downgrade because Sun City resort cannot sustain a 4mbs. I was never advised about this when signing the contract so I have been paying for a service that was never delivered. I had once again called to downgrade the contract and I was advised that my downgrade has been processed and should take a few days and that I will also receive a credit. We are yet again still waiting for this to be done 3 months later!! On my last call I advised the consultant "Yonella" that I will not make any payments until my problem has been resolved. How can I be struggling like this for the full term of my contract! This is a breach in contract! How can Telkom expect me to pay for a 4mbs line that is running at 0.2mbs?