Incorrect invoice and billing

Cell C is billing clients incorrect amounts that are accumulated due to their incompetencies. Apparently they were running a promotion on my account where they would load a data that is supposed to expire on a certain date fir some reason they did not set the expiry date and I get to be billed for it. I contacted them immediately when I realised that they will be billing me 42%. First they told me "but you also used the data" like really who asked them to run promotions if they were not capable of handling them. They are now telling me they will crefit it on my next invoice but what about the other Debit Order that was rejected because an extra amount that was budgeted for. If you are a Cell C client look closely at your statement they don't know what they are doing and you pay for their errors.