When you are dealing with seriously corroded galvanized steel, temporary fixes using couplings and clamps are absolutely not appropriate for a pressurized water line. Even if the original valve was failing, patching the leak with flexible tubing simply shifts the problem; the internal pitting is going to compromise the entire run eventually, and you risk a massive failure down the road. This is not a scenario for short-term solutions. My experience suggests that if a section of pipe is nearing the end of its life, the only correct path is a full replacement. If the stub pipe is too deteriorated to accept a standard replacement coupling, then the plumber should have been cutting and threading back to the last stable point, or ideally, using a proper fitting that interfaces with the existing material, but cutting is usually best.
If a contractor causes the damage while doing unrelated work, hold firm on accountability. The cost of the proper repair, not just the patch, should be covered by them, as the damage occurred during their service call. Document everything, including the specific type of repair they implemented and why you believe it is inadequate for sustained use.