MTn charging for returned non functioning router(poor service)

i took an mtn home router ,which initially they told me that it has coverage on the area where i stay.i received the router on the 03/08/2026,and it did not work,called the customer service to check the problem,and they could not help me until they told me to return it back to the nearest mtn store within 7 days to avoid cancellation fees as it is not working.i did take it back on the 08/08/2026 to Bethlehem down town mtn store as per mtn customer service instruction.it is month end now ,then i am being charged for the router that i do not have it at hand,i could not use it,it did not have network,a whole R800 extra on my account. and this is not the first incident with mtn,i do not know why did i give the second chance because last time they upgraded the wrong number,as i write this,i am paying for two contracts instead of one.and they could not help me because they said that i realised too late (after 7 days).The even weird part is that they use the same debit order mandate for 2 contracts because the initial mandate can only debit a certain amount that they cant debit all at once.