The OP should have asked questions before hiring someone. I'd consider
it an expensive lesson and remember to do your homework before jumping
in.

Get at least 3 estimates on something like this in the future. I wonder,
was the plumber asked for a ballpark price at all. If not, I'd say you
gave him a blank check.
And he should have, at least, kissed your mom on the lips after screwing
her...

CP