My response to your former boss would have been as follows. "**** you, your mother, and the horse you rode to work on"

They should have just stuck with you

It sounds like this company is very badly run, unprofessional and disorganised. I think you had a lucky escape OP!

So... Did you tell your ex-boss to go **** himself?

What a perfect time to tell your old boss to go **** himself with a cactus.

Welp, it's his problem now. Shoulda said something beforehand.

gah if he thought your work was insufficient then why TF did he have you TRAINING a newbie? your boss sounds like an idiotic asshole who needs a swift kick in the behind

They hired someone to replace you because they didn't think you did a good job, and they got you to train the new person on how to do the job? That just sounds like terrible management to me. If they didn't like how you did the job they shouldn't get you to train someone else. Additionally, it's not your job to train anyone how to do their job.

We need more info OP: How long had you been working there? What was your job? Did anyone ever complain about your job performance or give you a job review? Did you have a personality conflict with anyone at work? Was your training lacking too and if so did you tell your boss during that phone call? Is there a coworker you can talk to confidentially to see what you could've done differently or what specifically you were doing wrong? (To improve on for your next job) It's a shame your boss didn't give you any specific reasons as to why he thought you were so terrible at your job and why he didn't even want to try to help you improve he just wanted you gone. Hope we get a follow up. Better luck at your next job OP.

I would have simply said "I don't work for you any more." and put the phone down.