Zenni Optical Sent me unusable prescription glasses and refuse to refund me in full

I bought a pair a multifocal glasses from Zenni. The prescription was confirmed as entered correct. What I received was not fit for purpose and unusable. I ordered another pair with same size and shape frame from another shop with the same prescription and they were fine. Only the ones I made through Zenni were unusable.

I sent the glasses back out of my own pocket only to be told they were done right, which obviously cannot be true because otherwise I could see with them if they were. Zenni came up with excuses of frame choice which do not make any sense because when I made the glassses in a very similar frame they were fine. Even if the frame I chose was not suitable, they should have at least let me know - they are the eyeglass specialist, not me. I do not beleive the frame is the issue, just an excuse.

They refuse to refund me in full, only offering me 50% and no refund for shipping (both ways). They also offered 100% refund of just the glasses (no shipping) if I chose to risk buying again from them and accept store credit.