I question 10 days for a stop payment. Depending on the size of the company and the business that they do with the bank, it should get done quite quickly.
I would go to HR and demand that they stop payment on the check and issue you a new check. If they are reputable, they should do it.
As for Comcast, I was supposed to start working there a while ago but I got called back to an old job for the time being. That and I have a lot of work to do around the house. Once I start working there, maybe I can speed things up a bit for those with them.