Broken pivot bar of vinyl double-hung window lower sash

Hi - I have a bright white vinyl double-hung window whose bottom sash needs repair. The part of the frame where the pivot bar is screwed broke. The entire window measures 29W by 46-3/4H (from jamb to jamb), the lower sash itself is 27-1/8W by 23-3/4H. I already cut the channel at the top of both sides to replace the shoes of the lower sash and I'm now looking to fix the sash itself.

I tried the following: (i) I tried to glue the frame back using different variations of epoxy but it failed (too much force exercised on the pivot bar). (ii) I tried to look for a replacement sash but can't find anywhere a brand logo or a reference number.

So at this point, I'm interested in your expert opinion on what I can do.
And finally, I'm looking for a channel blocker to protect the part of the channel I had to cut.

Thank you!