Sigma ac111 fob not working, alarm continually gong off?

I have a 52 plate ford transit with a sigma ac111 key fob, the one button type. I do not have the keypad fitted to use with this. Nor do I have any other spare keys or any codes. Basically when I bought it I wasn't made aware of any codes etc that would be required. Recently the fob has stopped working and the alarm is going off when the doors are unlocked manually using the key. Opening the van this way doesn't open the side or rear doors. Does anyone think tht this may just be the key fob tht has worn out and a new fob will fix the problem. If not does anyone have any advice or similar experience. Can anyone supply me with the code I need to reset this and any programming advice. Many thanks. 07919352239