For some reason the transmission shop keep's saying that they haven't been able to replace my TCM/transmission control module because Mercedes keeps giving them one's that do not work and are "defective".
What's the deal here?!

this sounds like local dealer is not working well with your 3rd party tranny shop for genuine parts BUT tranny shop has no obligation to buy local.
They can ship from across the country mbpartsexpress dot com or any others genuine online supplier...

Besides rarely TCM go bad but often "conductor plates" do and get replaced with clean solenoids.

Get online yourself and do some homework with pricing then call tranny shop before this all goes out of control...

Shops that service and repair MB transmissions need a yearly software license from MB in order to program replacement trans modules. I would doubt this repair ship in question has that licensing,

New conductor plates on 7G and newer transmissions must be purchased and installed by the dealership (or licensed shop). Apparently, they will not sell to individuals. This is because the TCM and conductor plate are anti-theft items and the buyer must be verified to be the authentic owner of the vehicle. The older 5G trannies do not have this "feature" and can be bought online, such as from ECS Tuning, FCPEuro, etc.