They have my money, I have paid but not recognised.

I get an invoice, EFT reference says X.

I make payment with reference.

I get invoice, payment received, -R766.70. Now I owe double. Yes, somehow my payment became a negative balance.

I stop getting invoices, get sms, you owe us money. Granted, I forget to pay this month. So I pay quickly but notice, the amount out standing is last months + payment received + this month's out standing.

So I question it online, get told my reference (that is on the invoice and has never changed ever) is wrong. They won't recognise my payment. So I ask, how do get my money back?? I start asking questions. The online chat agent shuts down the chat.

Now what??