Please transfer the refund for the returned item to my account.
Literal
Returned item's price [object-を] my account [to-に] transfer please.
振り込む is the standard verb for bank transfers — a practical word for anyone dealing with Japanese banking. 代金 means 'the price paid for goods,' more specific than 金額. The relative clause 返品した modifies 品物 — 'the goods that were returned.'