how to fix my sigma car alarm?

I have recently bought a vauxhall astravan with a sigma m car alarm added. when i prees the key fob to arm the alarm the light on the key fob flashes but nothing else happens. the company i bought it off say it hasent worked for a while and they do not know the code for the key pad. could you advise if i can fix some how or scrap and by a new one. many thanks. brian kelly