MTN Debit Order for Cancelled Contract

Migrated from Business Contract to personal due to overbilling - I paid over R10 000 for 3 months without any explanation.

The migration was confirmed as successful, but a year and a half later (after paying for airtime and data top-ups only to avoid issues) they've debited a lumpsum for unpaid Business Contract because they left it active.

I've dealt with their call centers that pass me back and forth from Prepaid to Business, I've contacted them over email (***, ***, ***), I've contacted them on Facebook. Nothing helps or resolves the issue.