Ridiculously Unstable Arrears On My Acc!!

We received countless messages stating my mother's acc is in arrears and has been escalated to the relevant bodies. Now my mother has been paying her acc on time until she was told she owes +6k to 7k in a space of 30days when she didn't even buy anything from the store with her acc store card. We enquired about this sudden increase in outstanding balance and we were told that it's arrears. How did we move from -1k to +6k in just a month??? Which store accounts arrears of +6k from their customers in 30days? We told the office to fix their mistake which they didn't because now we have received an SMS stating legal action will be taken against us since we haven't made any payments to the acc to clear the outstanding balance. You fail to provide us with a detailed statement and on a month to month basis the amount of arrears added fluctuate ridiculously with no real explanation. This has been on going for over a year and no one has been assisting us. I am beyond disappointed and I wouldn't advise anyone to open an account with Jet. They are unreliable, slow to process important matters impacting their customers. This truly shows where their priorities lie, with themselves, with their own pockets!!