More money after debt was settled

My Father in law(age 80) was in Hospital in May 2018 and had to receive a neck brace. This was apparently not covered within the in-hospital benefit. He had no calls from Kachelhoffer Orthopeadic Services and has received an sms ones from them in April 2019. I have tried contacting the number provided at the time and there was no answer. I googled the service provider and sent them an e-mail. Kachelhoffer then sent a statement in April 2019. My Father in law was admitted to Hospital again and we had other important things to worry about. My Father in law received a call from the Debt collection department and as he is old he didn't want to provide them with details. I paid the account end of October in full and now received a e-mail stating that my Father in law owes another R140.85. A whole month and 4 days later we got told that he owes another R140.85. Seriously, where must he get the money from? And to hand someone over just like that, he has not received one account from them the address and contact details where on the statement. This is really a company that does not care about the elderly. If they had trained staff that knew how to speak to older people he would have paid this account long time ago.