Driveline vibrations are def the worst possible thing to diagnose.
They all start with a wheel balance and rotation, it just escalates from there to real work and measurements.
If I can offer any advice in this scenario, be as non confrontational as possible.
Bring them the facts about the situation and ask them for help to fix the vibration.
When you start the conversation with a shop that "they messed up", it always puts them on the defensive. Even if they are...