No idea whats happening with RC891367765CN . Please help

Divya, I couldn't find any result about your package. When was your package sent out? Usually, the tracking information can be found out in 2 or 3 days after it was collected by China Post.

how do i find when was it collected by china post? As it just shows this tracking number

The tracking information will show when your parcel was collected. However, there is no result after I tracked it with your current tracking number. I am afraid that this tracking number is fake.

What should i do in this case... :( Did they cheat me?? How to get my money back?

I am not sure if you are cheated. If you paid via Paypal, you needn't worry about it. As far as I know, you have sixty days to open a dispute and claim your money back. It usually takes a month. After waiting a month, you may open a dispute if you still don't have the package.