Over charged debit order by R530

Over debited by old mutual by R530 its been 3 months since i put compain about amount that im over debited they can't explain where the money is going they keep on saying matter is being investigated but every month im being debited for the amount that i don't know where is going very poor service how can they take so long to figure out where are my debit orders where are they going im very disappointed the way this big company i trusted is doing things all i want us my money back please