I have to second the idea of a certified letter:
I had a situation very similar to yours with Symbol (bar code scanning company) My little dance with Symbol lasted nearly 4 1/2 months of sending in the same unit over and again.
Eventually I got fed up and sent very detailed certified letters to the COO and CEO at the NYC offices of Symbol Technologies informing them of the terrible customer service... Come to think of it the repair facility I dealt with was also in Texas... Wonder if it's the same folks?
Anyway, we finally got some results by getting our original unit repaired and a second back up unit ($600) at no charge and a personal apology letter from the COO. All within 5 days of mailing the letter.
In situations like this email is NOT the way to go. Try a snail mail letter to top brass and see if you get results.