Question : How to stop theft of services?

I am a computer guy who fixes computers.
I have had a quite a few clients who have not paid me in the last year and i am ready to do something to insure they pay me.
I am looking for a program that i can install on my client's computers that will allow me to disable their computer if they do not pay.

Is there such a program?

Answer : How to stop theft of services?

Hi,

ACL 102 is not permitting vpn
you need to add:

ip access-list extended 102
 1 permit udp any any eq isakmp
 2 permit udp any any eq non500-isakmp