Hello JOHNNYL,
I could be wrong but the most likely reason that your ISP was able to track your activity while using IPVanish would be that you have a DNS leak. It's simple enough to find out whether I'm correct. Just go to this website whilst connected via IPVanish: https://www.dnsleaktest.com/
If any of the dns servers listed relate to your ISP then you do have a leak. According to the IPVanish support pages their software should prevent this from happening and force the use of their own DNS resolvers but perhaps you are not using their software. Either way, if the test confirms that you do have a leak I would suggest manually changing your primary and secondary DNS addresses through your computer's network & sharing properties to the IPVanish ones of 198.18.0.1 and 198.18.0.2. Alternatively use open DNS addresses, anything except those assigned by your ISP. Actually it's probably better to use something other than the IPVanish ones because their website does say that they only work whien connected via IPVanish and you'd need to keep changing them back whenever you weren't using your VPN connection.