Jammed throttle?

Hello all,
I am a new and absolutley clueless scooter owner.
I have a puch zip fast rider.
I came off it twice last night and am sitting with a sprained wrist and torn knee ligiments.
WHY?
The throttle jammed on full when I was at a roundabout and I hit a cyclist ,luckily only nudged him, but I also nudged the ground harder.
after all the paperwork etc I got back on and rode slowly to get back in the way and after getting safely on the bike path (im in Holland) the thing jammed itself up to full hrottle and threw me off again.

Question is WHY?
I need it for my work when I am better
Thanks anyone