Rain 5G uncalled for billing

12 of May I paid R999 upfront for 5G for the month, which serves as credit for 30 days, they tell me my next invoice will be from the 12th of June to the end of June which will be adjusted and then R999 on the 1st of July as it should be. on the 1st of June I got billed R124.50 for no reason and a ticket was issued to their billing department and i haven't heard one thing back from them. Sort it out.