Harassment!!!!! ?

I've had a SIM card data contract with Vodacom a few years ago. I cancelled it as I moved overseas and had no use for it anymore. I got an email stating I should pay the full contract amount. When I went to visit last year June (2017) I went to Vodacom in Cape Gate, Western Cape to pay the FULL amount. In July 2017 I went to confirm that I no longer owe anything at the Vodacom in Woodlands, Pretoria. They said my account was paid in full and that my cell number has been cancelled already.

Now since September of last year (2017) until as recent as yesterday (24/02/2018) they have been calling and sending SMS's to my MOTHER-IN-LAW...... They have been harassing her, saying they are going to send me and her to jail. I don't even know how they got her personal contact details. I've emailed Vodacom about this and even posted on Facebook, with no response. They just keep harassing my mother-in-law. They've got MY email address so why isn't Vodacom contacting ME? I am not in S.A. at the moment, so I can only be contacted via email.