I think that might just be an individual faulty case that doesn't fit.
We had ordered both black and clear cases. The black bottom case didn't go on properly; the clear one slid on fine.
All the videos I've looked at show the bottom case simply snapping on, not sliding.
Really, if 10 tries doesn't do it, they did the right thing with the refund.
There are some great, if expensive, hard cases in this thread that no doubt would work better instead. And more coming... all too late, I realize. I'm glad to have the temporary use Mosiso though until a really nice hard case is available.
When you slide the case from the bottom to the top(The clips being put on at the end Im assuming) on the sides where the ports are, if you try lifting it will it lift up or is it firmly attached? What is weird is that the top of the case is absolutely perfect zero issues and Ive bought from this company before when I had the 2018 macbook pro that is why I went with them again..I got the pink case with them, the chalk pink..he sent me a replacement chalk pink case plus he sent me a replacement bottom case in clear color not sure why but he did..yeah in the past Ive never had to slide in anything before, just pop it on you hear the snaps and thats it(In fact even now when I connect it I hear the snap but on the sides of the bottom case you can still pretty easily lift it if you wanted to its not a secure snug fit)