I'm not following here. Is the NM-B in a wall ? If it is tacked on to the drywall, you get to take it down and start again. I'd like to see a photo of what you have at the moment.
By the way you have another option here if the NM-B is correctly installed: keep the 8/3, change the breaker to 40 Amps, and run power at 32 Amp continuous. I'll leave it to you to decide how much to pay the "electrician."
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Addendum: I have no idea about TX. In NM we have licensed electricians and handyman. The latter are not allowed to install conduit. I don't know if they are restricted to a maximum AWG wire, but it seems likely.
Addendum #2, general FYI:
A branch circuit (BC) used for EV charging is continuous use. The wire and breaker ratings must be 125% of the maximum power draw. NM-B wire ratings are per the 60C column in table 310.16 of the NEC. Corrections and adjustments (e.g., due to high temperature) are per the 90C table but that is probably not in play here since the 60C requirement will likely be the deciding factor. Very hot places may end up with a different result.