I have a customer with a CTX 100 system at one point in time they had multiple stations that would all ring on incoming calls. About 2 weeks ago a lot of those phones quit ringing. I went into the system programming and checked these sets and they are programmed to ring. I have a set that does ring on incoming calls and if I change it to not ring in programming, it still rings. I have reset the system, reseated the cards and am not sure what is next. Help Please