Why can't we keep our old home phone#? ComcastKenF...please help!

ComcastKenF, you're our only hope!!

Comcast won't give back our home phone number that's been with us since 1987.  My sister took our home number so that my dad who has dementia is able to recite this number in case he needs the nursing home to call.  It's also listed on my parents' medical, medicare and other institutions records so this is a huge deal.  Comcast c/s claims they can't get the number back because she's change blling/service areas.  My sister had been able to move the number back and forth from different zip codes several times in the past, so this issue appears to be a clerical error of some sort.  They're offering $100 credit for our troubles, but doesn't seem like they're all too interested in helping get our number back.

Any suggestions on getting our old number back?