Actually- this is great news. It means you are finally coming to an end of your issues instead of just guessing!
Bad news is that it might involve spending a bit more money(depending on your skill level and how much you want to get involved).
Yup - My SWAG is that your brushes are stuck (or fully worn out?) and not making contact with the armature inside the motor. It is totally fixable but probably not something that the beginner can tackle and it may involve some special tools. A guy named Andy just did this and posted pics on FBook gem forum. Here is the link to see if this is in your wheelhouse.
If you have time in the next couple of days, at least pull the motor (which you have to do anyway) and remove that band cover at the end of the motor. Get a good look inside there and maybe send me a few pics if you don’t understand what is going on in there. You could get lucky and they will only be slightly stuck. Unlucky would be really stuck. (the guy in the link above had to use a c-clamp to press out his brushes. They must have been scary tight!).
Option 2 - find someone in your area that can rebuild the motor for you. I have no idea what it will cost. I saw a comment elsewhere that sometimes it may cost as much as a new motor, but that was from a company that sells motors.
Option 3 - find a used motor. It just happens that there are currently TWO available from guys in this forum. Since they are from out of state, shipping will need to be added. Here is the link to the first post. Down at the last post you can find GrantKC has one also. Both of them sound like pulls from very low hour cars. This might be a viable option for you.
Option 4 - Ask yourself what are your plans for this car? You may want to take this time to upgrade to a higher Hp motor. But that will require reprogramming the controller(your favorite) for best performance.
When it comes to removing the motor-
*** Tip ****
Whenever you take a cable off any of the motor lugs you should use two wrenches(one below the cable end and one above). You might need to find a thin wrench to do this(which not everybody has). Don’t be tempted to just wrench that top nut off. It can spin the stud in it’s plastic insulator and crack the insulator. Same goes for tightening.
*** BACK IT UP WITH ANOTHER WRENCH!!! ***