Disgusted

Hello. My grandfather has a landline nr with Telkom. They upgraded his landline to use a sim instead of the wired one. His contract pm would bd R250pm. In May 2021 the bill was more than R900. Upon enquiries they said someone took out the sim and bought data, but the sim was locked to be used in that phone only. We asked them to give us the nr the data was bought. To our surprise they do not have it on their system. Weird right? My grandfather paid his usual R250 in may. To our surprise in June 2021 the bill was R3000. They did not pay and they cut of the line. Now the bill stands at 3.7k even though it is cut off. We want answers. Is this how they treat people over 80 years old? The nr in question is ***