unbelievable, not refunding money

long story short, first they disconnect your line without any phone call or anything... then advise you they tried to deduct funds, which was the wrong account. then they say there will be refund after debit order, to date they have not paid the funds that is in credit as they advised, meaning that they are not keeping to their word and this is not acceptable this for a client that is with Mtn for 20 years