Over charged on account

Vodacom has been charging me a “Handset installment” where they weren’t meant to... I contact them and they agreed that they were in the wrong and said they would credit me the money (This took about 2-3 months) After after about the 5-6th time I called I’ve now been told that the money was paid to the wrong person and now they will have to investigate why this has happened. The amount is just under R1000 that they owe me.