The only thing I can think of is - initially I created an image of my old 128BG SSD and then extended the partition. Could this be the reason and how to fix it?
I don't remember exactly, most likely Acronis.What did you use to image and clone your previous drive?
No problem reported and the store refused to exchange the drive as I bought it more than 1 year ago and asked to bring it for repair. Which I believe would not help.If it reports problems and the drive is still under warranty, get it replaced.
It just sounds like you have 1 128GB partition, and the rest is not formatted.
disk cleanup should have cleaned that out
A clean install solved the problem