Lost bezel.need new one .where can i get one?

whats the problem are you trying to fit the new bezel? you will also need to ensure the bezel retention spring is with the bezil

These bezels sometimes get clogged with dust and dirt, it will need to be removed and cleaned, there is a small spring underneath so care must be taken so it is not lost while removing the bezel

YOU have to buy new one. Will be costly. Check out e-Bay. Cheapest prices are there.

You'll need a watchmaker to fit the new bezel. If it is just scratched I wouldn't recommend fixing it. You may pay 50$ for the new bezel and a pressure check; that may not be economical.

Try parsecent.com, you can get a replacement bezel there...

and you are right, you are basically buying a new watch as this model is made of plastic and cannot be 'polished'. Refurbishing it means that it will look new and everything on the outside would have to be replaced...good luck :)

buy a new watch

Yes, there are solution for that, but you will not be able to solve it yourself as the new part is needed.
That new part is called BEZEL SPRING and it is fitted underneath the bezel.
Bezel spring has special hooks pressed into it and allows to turn the bezel one way only (anticlockwise), at the same time stopping the bezel to turn clockwise.
Another cause can be that the dirt and grime are collected between the bezel and the watch case (this is where the bezel spring is located) and is stopping functionality of the bezel spring by leting the bezel slide over the hooks. This can be fixed by cleaning the watch case in ultrasonic cleaner.
Anyway- if the bezel is rotating on its own, I suggest that the bezel spring is broke and you will need to replace it.
Do not forget to rate, please.

If you've been trying to snap on that bezel and it does not stay in place, you probably lost the bezel fixing spring.
Find your nearest watchmaker and ask to sort things out.