I replaced PRI service with AT&T local with a PRI from BellSouth. Now the end users on my Merlin Magix can't conference. BellSouth says it is programming in the Merlin. We switched because we were having problems on AT&T with 1 way transmission (they couldn't hear the callers sometimes) It is a problem we had at 4 other sites. Now we have this new problem. What could it be?