Remote Central Locking Problems - Seat Ibiza

Hey guys,
'I've been having some issues with the remote control for my car's central locking system lately. I can only open or close the car if I'm standing quite close to it, and not from every angle! Sometimes I think I have an infrared remote instead of a radio frequency remote! I've already replaced the batteries in the remote and checked the contacts, everything seems to be okay! Before, I could open or close the car from a distance of 15 meters, but now I can't even do that.'
The car is a 1998 Ibiza GT TDI and has the standard VW remote control with an alarm function. It would be great if you could help me!
Regards,
Monchi.