I listened to a lesson in turkish and when the speaker said the turkish word for "husband" he said something like "Kocanız" and not "Koca" as I expected.
Can someone tell me how to write correctly the word "Kocanız" and why the speaker did'nt say just "Koca"?

you've written it correctly
kocanız means "your husband" (the formal, polite form of "your")

is it right to say (karin =your wife?)

yes, but I've seen that men use mostly the word "eş" (eşim, eşin etc), maybe it's a more polite form, right guys?

Thank you, Layla.