FXS problem TDM400p

hi i have a tdm400p with 1 fxo and 1 fxs
the fxo all works fine,
the fxs port has got a phone plugged into it, and i can call it from my other SIP and SCCP phones

when i use the phone on the fxs port i get dial tone and i can also hear dtmf when i enter digits.
however nothing happens
no call is made, dial tone continues all the time i enter digits
asterisk detects the fxs is off-hook but does not seem to get the dtmf for the digits.

am i doing something odd here ?

found the solution
i reduce the gain of the fxs port and it solved the problem