Incorrect billing

I signed up with supersonic and my router eas delivered 6th April 2020, i paid the R399 "activation fee", let's just say since signing up it has gone downhill. I was told i will not be charged for May 2020 but when i received my invoice at the end of May 2020 the normal amount for june was on there, as well as the R399 for May 2020, but a credit note was sent for that. Yet when it came to my debit order.. The same R399 they sent as a credit note, was added to my debit order. Now i can't get hold of anyone on watsapp, its like they dont exist at all. I want my account reimbursed for that R399 they STOLE. Can't even get through to their customer service. You'll stay on hold for the remainder of this lockdown. To add the cherry ontop. When complaining on their Facebook page, someone comments and asks for u details so they can sort it out, yet they never get back to you. Never recommending anybody to uselessonic.