I learnt English in the USA = I have learned the language when I was in the USA. This sentence makes perfect sense! I've English in the USA = I have English in the USA, which doesn't make sense! I've been learnt English in the USA = also doesn't make sense, unfortunately! You could say I've been LEARNING English in the USA, which means I have been learning English in the USA, as in you have been in the process of learning English in the USA. Hope this helps!

Note that in the U.S. we don't use "learnt" We'd say, "I learned English in the USA. "

Remember that "learn" is the opposite of "teach" in English! I know in some languages it can mean both (similar to "The fish is cooking" and "I am cooking the fish"), but not in English.