“Oh, hey Debbie. Sorry, I meant to call someone else.”

You wanted to call your friend, but instead you called your landlord's phone number instead by mistake. You know your landlord pretty well. When she answers the phone, you say:

Oh, hey Debbie. Sorry, I meant to call someone else.

Oh

You say "oh" when something surprises you.

hey (name)

You say "hey" to people who you know casually when you first see or speak to them.

Sorry.

This is a way to apologize for a small mistake you made. When you make a larger mistake and want to apologize more strongly, you can say "I'm sorry for ___ing":

I'm sorry for calling you by mistake.

However, in most situations this would be much too strong of an apology. So just saying "Sorry" is more appropriate.

(someone) meant to (do something)

When you did one action, but you wanted to do something else, you say that you "meant to" do the 2nd action:

Sorry, I meant to call you earlier but my phone died.

"Meant to" means that you planned to do something but didn't succeed.

someone else

This means "another person" but "someone else" is a more common way to express this idea.