Double charged for an LTE router

I'm so disappointed in MTN. My account has been debited even after I had paid via a payment link. I took up a new contract with them last month hoping for peace but a can of worms I bestowed upon myself. I have been telling them that they were not supposed to debit my account and asking them to reverse my money but to no success. This has been happening since the 1st week of August. We are on the 29th already and still no feedback. I'm certain that my account will be debited again on the 5th of September even after the Debit order had included the September subscription. Please help me sort this out.