That deal seems to have long expired at Lidl, so I can't find any specific information on that receiver. Is there a serial number or any other identifying information on the unit?
Lidl might be able to put you in touch with the manufacturer to order a replacement remote control. Alternatively, you could buy a cheap universal remote and use that to control it, but you may have a problem finding the appropriate manufacturer code — you could always ask in a shop to see the universal remote manual to see if your receiver is listed before you buy.
Incidentally, I've found the
One For All telephone support people to be extremely helpful in the past when it comes to making their universal remote controls work with certain equipment, so that may be a brand you'll have more success with if you choose to go down that route.