Clearly, I've missed something here...Follow

Unless you're broke, I'd hazard a guess that you're somehow bugged. Unless you're already at the next rank and didn't notice, which I rather doubt. Probably need to petition a GM.

You should need to buy the expert skill level. If its really missing from the trainers, theres a problem. Have you checked to make sure you have the trainers showing "Available" receipies? It may look like you have nothing to train if somehow only "Unavailable" is checked, or both are off.

Tsarduccl probably has it right , a few times i have thought WTF ? and then checked up here and should be able to get the next level , and then realised i had clicked off the available skills so i could not see it in the trainers list , make sure its a trainer in a main town you go to as well as i am not sure if all trainers can upgrade you.

If after going to a trainer and checking again it still does not show then ask a GM as that is the only other choice.