A. "Hi, I want to tell you I get that job!"
For you to be able to tell me - at this moment - that you have found a job, then you must have found the job before this very moment, that is, say, yesterday - that is, it's past. So you must use the past tense.
'I want to tell you that I got that job.'
or
'I want to tell you, I did get that job (that I was telling you I was going to apply for.)
B. "I knew you got/get it."
'I knew when I heard you were going to apply/going for the interview, that you would get it.'
or
'I know. I heard that you had got it.'