It could simply be that the remote needs to be un-paired and re-paired.
You could try and find a Logitech Harmony remote (these can download the IR commands which control the Sunrise/UPC TV Box) but they’ve been discontinued so are hard to come by and probably not worth the cost now. Which is a pity as they were good.
You could research Sofabaton. I’m not sure if they have the IR commands; you’d need to check. However, don’t spend too much because Sunrise’s newer boxes, thje IP TV ones, have no IR capabilities and there (currently) appears to be no way to connect third party remotes to it using bluetooth.
One final option is to buy the cheapest programmable remote there is, and find someone with a Logitech Harmony remote, and use that to teach the programmable remote.