Unauthorised Spend imit

Hi, When i took out my contract with Telkom, we set my spend limit to R0.10. All went well from March till July 2019, and now in August, someone, without my consent, increased my spend limit to R1500.00. Telkom did not/cannot prove that I increased the spend imit, and I did not. Now, I am being told that I am liable. Telkom is truly *************. Telkom Reference ***9 Regards Mr K.Pillay ***