Can you solve this? Smart Car tries to move while in neutral.

I have 2009 Smart ForTwo 451 with some strange behaviors. Do you know what's wrong with it?

Car will start, but when it's sitting in park it attempts to move forward. When the car is in gear you can hear the engine struggle to try to move the car, but it won't move.

Backstory: I had taken the car into Mercedes-Benz of Beverly Hills since the car was making a knocking noise. The motor ended up having to be replaced... so I did the work myself. However I had found out in that process that they stole the clutch actuator off my car, replacing it with a faulty one that was probably off of another one of their customer's cars.

I ended up replacing that myself, but now the car still won't function correctly. I'm not sure if the transmission is just seized from sitting for so long or if they did something else mechanically that has now disrupted the car to where it won't drive. Help!

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