My assessment.
You have or had two problems. The first was a leaking tub tap. That was the easy one and has been repaired.
The second problem is communication, the way people describe things and the way you read them. Plus the communication is coming to you through a third person. That is the most difficult part of trying to assist some one with plumbing problem here at AMHD. You really have to stretch your mind sometimes to grasp what the problem is.
with the hot water tap not being able to be closed
I would interpret that as meaning, not that the tap couldn't be closed, but that closing the tap did not completely stop the water flow. In other words the tap leaks. Remember this is coming to you from a non-plumbing person through another non-plumbing person.
Plumbers response.
"The hot tap which supplies the bath has been over tightened to the extent that there was no movement left on the tap spindle
Simply means that the tenant kept tightening the handle tighter and tighter to stop the dripping tap.
The tap was stripped down and reset before it was reassembled."
Plumber replaced all washer, "O" rings and other necessary parts. Hopefully he replaces the seats. Hopefully, he replaced washers and seats for both hot and cold sides.
Over time the water flow will corrode the surfaces of the faucet (tap) seats. When the tap spindle pushes the washer up against the seat to stop the water, the corroded surface of the seat wears the washer. As washer surface deteriorates, you tighten the spindle tighter, which further deteriorates the washer. Eventually tightening the spindle just doesn't work any more and you call the plumber.
This most often happens on the hot side before the cold.
Had your managing agents said, "You have a leaking bath tap", you wouldn't have been confused about what the problem was. A dripping tap is not an uncommon problem.
Had your plumber replied with,
"Hot side of bath tap leaking due to worn out washer. Rebuilt taps, hot and cold, with new washers, seats and "Hot side of bath tap leaking due to worn out washer. Rebuilt taps, hot and cold, with new washers, seats and " rings".
You would have felt better about the bill. Still just means he replace the washers but sounds more professional, is more descriptive and would have made you feel better about the price. That is, if indeed he did rebuild the entire tap.
Hopefully this communication is coming through with some degree of clarity. If not, post back.