Never ending homeloan

My mother has a homeloan with Nedbank. Since 1996 she has been making payments religiously, every month. Now she is retired and Nedbank claims she still owes R200, 000,00. 5 yrs ago they said she owes R120, 000,00 and today they say it's at R200, 000,00. How is that possible when no payments were skipped?? 5yrs of R7000 have not reduced the amount but has increased!! Today they are threatening to come for my mother's house. They sent an evaluator already. Is this fair?? In her late sixties my mother cld lose all her hard work. This can't be right.