Alarm help!

Merry Christmas all!

so my mk1 has a sigma s series alarm fitted.

it seems to be draining the battery as it goes flat after 4/5 days. Today after my husband tried to jump it it seems the key fobs for the alarm have somehow de registered.

this leaves me with a car that's immobilised but no way of turning the alarm off. I don't know the pin code and nor does the previous owner.

Any ideas?