I know I know it's not supported by vfx However

I have a monitored alarm that although it is not monitored I dial into it to change the configuration etc. And up until very recently
it worked fine, dial in with my laptop connect and all was good.
I am also an occasional fax user and used to receive faxes no prob, again recently I've begun to have problems receiving faxes,
either won't connect at all or drops out half way through.
Does any body have any ideas whats changed. My connection speeds all look good (Approx 2 meg) and the only thing I've noticed changed is some where along the way my router (Wag54p2p or something like that) had its firmware upgraded.
I rung cust support and they said I'm using the high bandwidth code thingy (very tech talk I know) and their wasn't much they could do.
Any Body go any ideas, Is it work rolling back the firmware, etc.
Nathen