The trainer should be increasing the level cap of the skill; you still need to put skill point in to raise your current skill level. If you have a level (4/5) for Magic Missiles, for example, and upgrade it, the skill should show up as (4/10) in the skill window.
If the maximum skill level is changing and you just thought he was increasing your current skill level, then you posted in the right forum. If you are learning skills but the maximum level doesn't increase, then that would be a bug (haven't heard of that, though) and could have been posted in the technical problems forum. It isn't always obvious which problems are just something being missed vs an issue with the game itself, so there is a moderate amount of overlap between those two forums, anyway.
Welcome to the forum.