Customer refusing to pay Bills

I am trader involved in wholesale trading of textiles. There are a few customers of mine who are unwilling to pay bills even after the expiry of stipulated credit period, repeated reminders, etc.
I don't have much hope from the traditional methods of recovery - such as giving a legal notice, cz it might be a lengthy and ineffective procedure.
is there any other recourse which will compel these wilful defaulters to pay up effectively.