Airtime purchases

I recieved multiple SMS's on my phone saying that I've purchased an outstanding amount of airtime at Mr Price stores on these dates:

11/03/2020 - R5 airtime 10/03/2020 - R5 airtime and R495 07/03/2020 - R5 07/03/2020 - R490

I do not know anything about these purchases on my account but Mr Price keeps on calling and threatening if i DON'T pay. I tried doing a follow up and went to Different Mr price stores to ask them to do an investigation but nothing has been done yet. I even went to the police station and did an affidavit. Lastly i went to my network provider MTN but they said they can't help. Kindly assist

Thank you.