A commmon enough complaint & usually the fix isnt too involved.
Let me guess – you have just one battered key so no way to verify if the key itself is at fault by trying your spare ?
Does key in drivers door operate central locking still ? Yes ? so the central locking itself is working. The physical key turn triggers the BCM ( Body Controle Module ) to unlock / lock doors.
The keyfob operation, relies on a good key, receiver, & wiring.
Often the keyfob’s ( blue 3 button remote ) buttons switches fail, & there are chaps on ebay that will test & fix the key with new switches & a cover etc for 30 quid or so. Maybe get a mobile locksmith to test the keys buttons 1st or supply a replacement / spare.
The key receiver is behind the headlining , front & centre, its only job is to recieve the keys buttons signal for central locking purposes , these can fail. Consider a used one as they rarely fail so used is a safe bet.
If all above checks out then test wiring (for continuity) from BCM to receiver.