Payment on eft

On the 21st of september i paid my woolworths account via eft. Until now they.re struggling to find my payment after i.ve mailed and faxed my proof of payment. Yesterday i draw an statement from the bank and they didn.t want that that as proof of payment. My account was paid up and just after i.ve contacted them yesterday they.ve charged me with interest. They also don.t want to refund my money...