Terminating contract

I have a WiFi contract contract which was supposed to be 600 a month but now they deduct about 2000+ a month every time I go to them there’s no solution they don’t seem to care they just keep saying the contract can’t be terminated,am very unhappy about this no one in the right mind can agree on 600 and end up with 2000+ we don’t even use the WiFi as the sim card card have a problem,they change the router still the problem is there.