CELL C WON'T CANCEL THE EXPIRED CONTRACT

My mom opened a contract at Cell C in 2018 and it was finished in 2020. We called to convert the contract to prepaid which was successful. We received an sms to confirm the contract was cancelled. Turns out Cell C was still debiting R250. We called to query, but the call centre consultant said we should ignore messages claiming my mom should pay R250. We went into the Cell C store last week (Westgate Mall) to query the matter. On the system stated R170 must be payed, which we went to pay just to get it overwith. The consultant sent the proof of payment away... My mom has received another sms that she must pay R250?! How long is this going to go on for?? Must we really get a lawyer now?? My mom is over 60 years of age, to deal with this *********** system.