No WiFi for two months

I pay a significant amount of money every month for a Adsl line that does not work. I have reported this numerous times without success. A technician came out, and after 4 hours he said nothing was wrong with the line, it must be the modem.I took the modem in to Telkom shop Centurion, where they tested it, and they confirmed nothing is wrong with the rooter. Since then i am trying to get this resolved witout luck. Just lame excuses. I want to cancell my sevice as Telkom is in bridge of contract by not being able to provide Ai service i pay for. I was informed i cant cancell the service as i have a 24 m contract., witch was extended without my knowledge I want to rather use my mobile data service, and need Telkom to cancell my contact.