Ongoing account problem

On 7 February 2020 my mom made a payment for the annual subscription in advance. They double checked the amount that has to be paid and she paid it into that bank account that she has always been using for years with no problem. The proof of payment was loaded on the account, but the payment never reflected on her account, or that is was she was told. In March she received a message that she owes the monthly subscription fee and her service was cut off. She phoned the call centre and told them that it is not possible and they could see the proof of payment and connected her again. They referred the situation to the finance department. After numerous phone calls and escalations she received another message last week saying that she owes another months subscription to avoid being cut off. I called the call centre myself and said it’s not possible and the agent saw that the amount she paid still doesn’t reflect on her account and escalated it to another department. I called again today to make sure everything is sorted and now all of a sudden she owes an enormous amount, which is again not possible as she paid a year in advance. It was again escalated to the finance department. How many times does a problem have to be escalated before a problem is solved?