Multiple issues, please help

[KaiserSoze]

I have a 49cc tao tao that started making a very loud knocking noise when running and driven. I read that it could be the "CVT" but Im not familiar with it so I decided to try an oil change first. Oil level was fine but a little dark so I went ahead and replaced it. All I had in my garage tho was 5w20 and like a dummy I used it thinking it would be fine for a trip to the auto parts store and back. Halfway there it started bogging down to the point it eventually quit running. At this point all it would do is crank repeatedly without turning over until the battery died. After getting it home and putting correct oil in it, it still won't turnover and starter solenoid plunger is stuck engaged with just a clicking noise. I have the crankcase cover removed exposing the solenoid. I desperately need honest advice on how to proceed. Thank you for any feedback.