Fradulent contract

Someone @ Vodacom fradulantly upgraded my contract using one of my numbers in Dec 17 and bought Cellphone and Head sets, my debit order went from R107 to R 1300 last month, this month was even worse they took R2 800, i had to reverse these unauthorised debit orders which is affecting my goodcredit score and causing charges , According to the Agent all this happened in Midrand whereas i was never in Midrand During Dec, i was in Middelburg where i initially took the first contact for tablets @ Game in 2021 & never upgraded since then. I need feedback as to how this happend how, who signed, submitted and whos documents where used for this upgrade, and cancel these fradulant debit orders on my account !