Refund overdue

They are claiming to have refunded me after the account I have with them was paid for twice in one month.I requested a refund of the second payment on the 28th March 2024.They claim to have refunded me,I sent them my bank statement which reflected nothing to date,yet they are failing to send me proof of payment despite their claim to have refunded me on the 2nd April.Pls help me get my refund.