Refund

I have had a very bad experience getting my refund ,based on the billing of my contract , I did a transfer from my personal contract to the business contract ,which left a handset installment to be paid off on my business account , however I was billed extra 3 months for the installment on a handset , I have since been asking for my credit back for the period billed ,I am being sent from pillar to post with 3 references from a store trying to help me S6-L6W2I-IACWD , S6-L3Y27-71NL2 , EC-293S-2NPIO