Trunks keeps open

Hi,

Im using Rhino 24FXO card with on board EC.
anyway, most of the times when i receive calls or even make calls through my outside trunks and finish the call the trunk never close. so when i want to call again or even receive call its always busy. so i have to login to trixbox FOP and physically close the line.
is there something i can do to make sure that lines hang up automatically after i finish the call ?

Thanks
Firas