My email is gone and for some reason xfinity can't get it back

I had a comcast email for about 18 YEARS and now it's gone! If you try to send an email to it, it will say undeliverable. When I try to add it back onto my account, it says it's already associated with the account. I've spoken with xfinity about it 3 times, the second time they gave me a ticket number, the third time I called they said there was no such ticket number and then they gave me a new one. This has been going on for almost 6 weeks now and has caused some major problems for me. Seriously, we have internet, cable, etc and pay a fortune every month - for 20 YEARS. This problem should not be hard to fix and I have to say the customer service I've received so far has been terrible. If this can't be fixed, xfinity I'm taking ALL OF MY BUSINESS ELSEWEAR.