The big (unanswered) question for me is; what is the final thickness of the drums now that they have been resurfaced twice?
If the guy only had to take off a very small amount to true them up, that might be one thing. If they required a significant amount of material to be removed and they are now close to the minimums, that would be unacceptable to me considering they are supposed to be new drums. Cheap drums or not, I expect a certain amount of life out of them and if they’ve been machined down enough, they may only last a short time in service.
At this point, I don’t think there’s much recourse for the OP. The work is done and the brakes are performing as intended. If they last through the warranty period, fine. If not, I’d demand a new set before I’d let them attempt to rework the drums a third time. Also, a closer look at the issues OK pointed out would be in order. It may not be the drums at all.