Supersonic wifi

I've been struggling to get hold of an agent to help me sort out the fact that my wifi has been suspended. I installed wifi recently and supersonic had a promotion of R369 per month for 3 months . I was on call with them and they told me to eft every month . They suspended my account because apparently i haven't been paying . I sent them all the proof of payment including my invoices which states I have to pay the promotion price . They are charging me the full amount of R699 for 3 months which accumulated . Each time I try to contact them it's a different person that I have to explain to over and over and I'm fed up