Bad design on replacement GE water filter head?

The water filter line coming from my GE Profile PSHS6TGXBDSS sprang a leak and that was when I found out that you can’t just replace the line, you have to replace the entire water filter assembly. Easy enough, I thought. The information in the fridge stated that the replacement part was WR17X11618. When I went online to order one for pick up from a local store the rep informed me that GE had since discontinued that specific model (the one that I wrote down from the information in my fridge) and that the replacement was now, WR17X22074. The rep confirmed that this was the information in their files, as distributed by GE, and the replacement would work (there was no other). Long story short, I ran into two problems when putting in the replacement. First, the water line leading from the (replacement) water filter assembly to the bottom of the fridge had a hex nut that seemed one size smaller than the original water filter assembly. Second, when I went to reinsert the water filter into the new assembly, it would not stay in place. After several attempts to screw it into place I realized the assembly-head was missing the ‘collar’ with built-in grooves that helped to guide the water filter into place, and hold it snug. I now have a replaced water filter assembly head and a water filter that refuses to stay in place when screwed in because it lacks the necessary supporting collar-and-grooves. What have I done wrong, here? Any help would be appreciated.