No refund received on items that were substituted - Very Disappointed

The other day I ordered off of the app, the order I made consisted of only 1 item as I wanted to test the app out and see how it worked. The item I ordered I was immediately charged for which was fine until they informed me that it wasn't in stock and that the item I chose as a substitute/replacement would be sent to me instead (which I later received - no complaints in terms of the delivery).

I didn't mind the fact that there was a difference but wasn't informed as to how and when I would be refunded the amount (which was fairly significant in terms of the order and the fact that I'm living off a student budget). I then lodged an issue on the app where I was told it would take 2-7 days to be refunded. I found this strange and was a bit irritated by the fact that it would take this long to be refunded especially since I had experience getting refunds from other apps such as Mr D and UberEats where it was instant.

Ultimately I accepted it and continued with my day - naturally going into holidays I forgot about it until today (2 weeks since the purchase) when I realised that I hadn't received any refund. I find this to be pretty shocking especially since I would assume that a big company like checkers would have automated processes for situations like this.

I'm pretty disappointed and have lodged another issue with them today to get a refund but regardless I won't be recommending them to others or ordering again with them anytime soon if I have to set reminders for myself to check whether I got a refund or not.