QUICK ANSWER
"No te creo" is a phrase which is often translated as "I don't believe you", and "¡Ja!" is an interjection which is often translated as "Ha!". Learn more about the difference between "no te creo" and "¡Ja!" below.
no te creo(
noh
teh
kreh
-
oh
)A phrase is a group of words commonly used together (e.g once upon a time).
1. (general)
a. I don't believe you
No te creo cuando dices que me odias.I dont believe you when you say you hate me.
¡Ja!(
hah
)An interjection is a short utterance that expresses emotion, hesitation, or protest (e.g. Wow!).