Both are fine. Though, in this case, "return your message" is better than "get back your message." You can say "Sorry, I've been busy and couldn't return your message." Or you can say "Sorry, I was busy and couldn't return your message."

Sorry I've been busy - this suggests that you are still busy. Sorry I was busy - this suggests that you are no longer busy. And couldn't get your message back - this part of the sentence is not clear and does not sound natural to a native anglophone. In lieu of saying this, I would say , " and I was unable to message you back" or "and I just couldn't find the time to message you back".

Sorry l was busy earlier

Sorry I've been busy - this suggests that you are still busy. Sorry I was busy - this suggests that you are no longer busy. And couldn't get your message back - this part of the sentence is not clear and does not sound natural to a native anglophone. In lieu of saying this, I would say , " and I was unable to message you back" or "and I just couldn't find the time to message you back".

Hi can i know what is the different between "been" and "was"?