Billing dispute

Hello Peter..Please help here i had contract with Telkom for 24 months contract end in October 2019. I keep contract on going because i was still deciding on what product to take. For the 24 months i have been using router when internet is finish i know is finished i will only connect the new month never had problem because i know my contract is limited . Before my contract finish i went to Centurion Mall Telkom and asked what going to happen if i don't cancel contract they said for router i will pay R200.0 and Phone i will pay R100.00 because it was two contracts that where about end. End of November i was debited well. Now i received statement there is extra R500.00 on my account that i don't know , I am advised that after data finished it was running but i had this router this thing never happen because i sighed for limited. I want to understand happen because if i'm ongoing contract it doesn't change the contract i signed with Telkom and it is not for the first time i experience this first i have to leave because they were referring to where i took contract.

Thank You