Hi Ukspud3,
It's a shame to read that you're having more issues with your Mac, but if it has been working before as you state, now may be the time to consider that the problem could potentially be beyond resetting the modem settings again and again.
As we've now exhausted all our support for this, I personally would recommend you allowing a Mac specialist some hands-on time to see if they can identify what's up and fix this. It's unfortunate, I agree, but unless you can pop the SIM into a mobile or another modem on another computer and it doesn't work in all cases (thus a network / account issue), the responsibility to get your Mac fixed does ultimately lie with you. There is only so much support we can provide without having your machine in front of us to get 'a feel' of the matter, and we're not Apple Accredited repair technicians either.
Keep us updated with how you get on, and if there's anything else we can do to help!
Daz
eForum Team