Hi! I'm new, so forgive me if I sound stupid. We have an Executone CX 816 system. I have a phone that was programmed 3 wks ago with 8 lines, now all of a sudden one line will not ring on the set (which is ext. 124). You can pick it up the line and get dialtone but when you call the number, it rings on ext. 100 on an unassigned button instead of ext. 124. Before this started happening, we had trouble "un-forwarding" the same line. I've pressed the MON key and then pressed the DND/FOR key, but it didn't work. Any suggestions??