I'm quite sure there is no such a mod, only those who change other aspects of leveling, but non of them STOPS it.
There is very quick and easy way of doing this in CS, you can do it yourself actually. I'd do it for you, but currently I'm having some problems with making Morrowind work on my PC.
Anyway, it's been a while since I had a look in the editor, but I think it's like this-
Up on the toolbar go to Character, then Skills (if not Character, then anything where you'll find skills).
For each skill there is a value of how much it will raise per which action. You can decrease those numbers, and 0 is, of course, no raise when you perform. Then you simply save it, name the mod, and I'll guess you know how to activate mods since you use them.
Hope this helps
edit: grammar