This report has some dust on it, so I don't even know if this is relevant anymore.
The remarks by "anonymous" are pretty much accurate. If the Chapter 7 was dismissed without discharge, then the debt is still collectable.
HOWEVER, if you received a discharge, and assuming that this creditor, or one of their predecessors was on the mailing matrix, you have stated a violation of the bankruptcy code.
So, if they are still trying to collect, I would NOT advise a cease and desist letter. Rather, I would send them a copy of your discharge order, together with a letter that any further attempts at collection will be treated as a violation of the Bankruptcy Code, U.S. Code Title 18, and any and all other applicable state and federal laws.
If, after receiving such letter, they continue collection efforts, I would either use your original bankruptcy attorney, or find another attorney who is versed in bankruptcy law, and file a complaint with the bankruptcy court.
Best of luck!