Selling support tickets

Hi,

I’ve been searching the web for a couple of hours now and can’t seem to find a good solution for my needs. I believe there must be a good plugin to achieve what I want..

Sell support tickets

For example:

40 tickets – 1 ticket = 15 minutes.

Whenever someone calls me or has something to do for me i reduct the correct amount of tickets from their support tickets.

There should be a very simple client area where the client can view their remaining tickets (and somewhere were i can deduct their ticket)

I have found some plugins with online support ticket systems but this requires the client to submit a ticket online; this is not what I am looking for.

Hope someone can guide me in the right direction.

Thanks!