I would not necessarily find fault with what any of the 3 guys did. It sounds like the 3rd guy appropriately upped the ante based on the fact that it was a recurring problem.
What seems likely now is that it is a bigger problem, either a defect in a pipe joint, roots, etc. The "local" treatments were partially, and temporarily effective. It would seem that at this time, it would be appropriate to have someone do a complete camera inspection of your line, to find out why the prolem is recurring.