I sympathise with the situation you are in, Ron. We all started somewhere, and it is very frustrating when there is no clear cause for an issue.
I don't know if a $15 Digital Multi-Meter (DMM) will help with this particular problem, but you will need one someday, and getting one now is a good start.
Second, throttles are pretty cheap, and I recommend that you purchase one from the same exact vendor so that the two throttles are the same, and the connectors are identical. It's not often that the throttle is the problem, but...it is the easiest component to swap-out and test. You unplug the mounted throttle, plug in the second throttle, lift the rear wheel off the ground, and then spin the second throttle in your hand. If both throttles had tested previously to work fine, then this test "should" show if the issue is the throttle or not. A one-minute test.
I have a small 6-FET sensorless controller from Lyen, and a larger 12-FET sensorless controller from em3ev. With either one, when I plug it in, I only need to plug in the three thick phase wires that power the motor. Almost all common ebike motors and controllers use hall sensors. This means that five very thin wires will also be coming out of the motor (three thick wires, and five thin wires).
There might be a problem with the hall sensors, and swapping-in a sensorless controller is a good way to test that. If a motor doesn't work with the stock hall-sensored controller, but it works fine with a sensorless controller? Then it is not the motor itself. It could be the hall sensors inside the motor (there are three). it could be the wires between the hall sensors and the controller (pinched wires that are shorting is a common problem), and...it could be a problem with the hall-sensor portion inside the controller.
If you get a sensorless controller for testing purposes, the throttle connector and the three phase wires will likely NOT have the same connectors on their wires, so...you may need to get a soldering iron and swap the connectors out for something that's easy to get, cheap, and works well. After soldering-on new connectors, you will need heat-shrink insulation over the new connectors.
I know you may be on a tight budget, but...right now this is the best I can do. You'll have to save up your money to buy parts to make each step needed...one at a time.
https://www.electricbike.com/connectors-halls-throttle-motor/
https://www.electricbike.com/matching-connectors-from-battery-to-controller/
https://www.electricbike.com/water-proofing-trouble-shooting/