Struggling pensioner

My mother-in-law had a drs account of R2500 - approximately, in 2017 after my father-in-law passed away. she is a pensioner and only receives a small pension including SASSA. she agreed to pay R100 per month cause that is all she could afford. now 3 years later with Van Rhyns Attorneys her account is R2900 approximately. she paid R2300 when I calculated it from the statement I received but they keep on adding fees and charges for smses and calls. even though she said that they don't need to call her to remind her or send her an sms, she will pay. she might have skipped a few months when things were tough, but really to milk an old lady like this is just inhumane.