Enable busy tone for second caller when line is busy

[emessinis]

We have a user in our PBX with analog line (single line) and we want to enable busy tone for second caller when line is busy.
Right now when the line is busy with external call and another external call comes in the second caller hears the phone ringing although is busy.
Allow camp-on is disable.

Thank you in advance.

[vad]

Your PBX - OXO or OXE? External line - digital or analogue?
If OXE and external line digital - manage users Public Network COS (Access COS) - incoming DID hold on busy set=0 and DID overflow on total busy=0