ok the incomming lines are not being translated to an extension via 3518 and 7600.
so your indial should match your numbering plan.
so 4 digit number plan your main line should be extension 6111
in 3 digit number plan your main line should be extension 111
I would run through command 10 or 14 and list up the Extensions find one that is skipped and program one in.
for example
10>001>f111
10>002>f112
10>003>f113
10>004>f114
10>005>f116
Insert f115 at an open lens. 9000>115,01> your prime line 93>115>115 then dial 850-6115. see if you get RBT and ring on the extension.
if that works find your highest Xtn number verify the indial , and I would have a base pool of numbers to work with. otherwise give the carrier a call and find out what numbers the customer has bought (usually in blocks of 10,25,50 or 100)
Regards,
Dr VuDu