My car alarm is not deactivating by my fob?

Other Category problem
1996 Vauxhall Astra Engine Size unknown Wheel Drive Type unknown Manual 150000 miles

my car alarm is not deactivating by my fob. I tried a couple of days ago to deactivate it with the fob the led light on the fob is working it took about 5 mins before it worked to deactivate it then a couple of days later after setting the car alarm overnight my fob would not deactivate it I replaced the battery in the fob still no joy.I rang green flag home start and he could not deactivate my alarm or bypass it as it was a scorpion and not vauxhall standard fit he tried the fob their was a slight dimming of the sensor light in the vehicle but no deactivation is it more likely to be a fob fault and it needs replacing?The car is immobilised