unable to use bought worlds

I'm not sure how to explain, but ill try my best.

I try to download a world (a free one, mind you) and it says its downloading. problem is it never goes anywhere. I have one that has been "downloading" for a few months, I forgot how many. id really would like to play some of the worlds, so please get back to me asap.

 

also I don't know the affected versions. I'm just an idiot.