MTN does not care about their customers

My mother is 80 and therefor her cellphone contract is on my name. Only I can give permission to change that contract. An agent called her from MTN and changed her contract, so now she can only use her phone between midnight and 4 in the morning! I have contacted their ***** department in February and was told the matter would be resolved in 3 to 8 working days. Nothing was fixed. I also contacted them on Facebook and every week they tell me that they will escalate the matter, but still nothing is done.