Business email down for 3 weeks

My business emails are down for 3 weeks and the Comcast technicians are still fixing it. They know what the problem is but it's the back-end office that has to fix the problem. Have no idea what back-end office means. Every time my clients try to send me an email they get an error "domain name invalid" and when I checked my email domain name on dnsgoodies.com website, it reports an error " MX record is missing". Everytime I call comcast tech, the answer they gave me is that my issue has been escalated as if escalation of the issue would help me in some way. Finally, my issue has been escalated to the level 2.5 so when I call them again to find out the status of my issue, I was told that once it reaches level 2.5 it's beyond their control; it's the back end office technician that have to fix my email problem. When I asked how many days it takes their back end office to fix it? There's no time frame for the back end office, in other words, whenever they get to my issue. After a week, I called the same number 1800-391-300 to find out if there is somebody I can call or is there a number I can call and talk to about my problem. I was told by the supervisor in a very rude tone or demeanor, "they will call you and I cannot get in touch with them".

Wonder How many weeks or months it will take Comcast to fix a simple email problem.

But most importantly, how long will my small business survive without email?