Billing wrong now they sending threatening SMS to a 81 year old lady

This department is totally pathetic they overcharge a pensioner off 81 years old now they threatens her with sms no stop. She paid her account since the 1st TV came out. R7.40 was added to her account for months adding up to R 199.90 No one seem to be able to the error. My mother have heath problems no she get all the threatening SMS Don't they have thousands off people that don't pay to go find. This is a matter of principals I pay her TV license on line it was never not paid