Hello Hisham I hope you're doing well. To answer your question the phrase "I hear ya" is not common nowadays anymore. "Ya" is mainly used with "What" nowadays. Like "Whatchya want" or "Whatchya doin" or "Whatchya up to" outside of these we really don't use it anymore.

'Ya' is a super casual, informal way of saying 'you'. So, I might say to my friend 'how are ya?' instead of 'how are you?' They mean the same thing, but it's a lot more casual.