Have you tried running different miners each time? It could be the that program you are choosing to use has been blacklisted and using another program in its place might yield better results. I doubt there is someone manually watching your actions on these VPS, and unless that is the case there are ways to mask your mining activity. It is extremely difficult to block mining, and much more feasible that only particular mining software has been blacklisted in this manner.

What programs have you tried? Which algorithms have you attempted?

I doubt that free VPS are intended to be used in this manner and you could potentially be breaking the terms of agreement. If you are breaking your agreement, then there is no reason to assist you. They might not want you mining on their company equipment, and therefore you should not abuse it.