Nothing is explicitly set to cache or not in IIS, when we use cache it is set on the page itself, and as I said before, if that was the issue other clients not using Vodacom also would have complained about this issue.
Well, the default is for pages to be cached. As far as I know, cache servers do not read the contents of web pages, so they will not even see your meta tags. You need to make sure your HTTP headers are set correctly. I don't know why other clients do not have a problem, but why are most other web sites working through the Vodacom cache?