Can no longer affect line created with shift

[Elia]

Hello!
I created a straight line using the shift,click method. Now nothing I do will affect it. When it failed to be made invisible by toggling the layer I thought I created it in I systematically went through each layer in the image, turning them visible, invisible in case I lost track of where it was created, but even though those layers became visible/invisible as they should, nothing happened to the line. I tried to create a layer above it to just cover it up, but even though the new layer was on top, the line showed through. Although this line used to be needed it is now essentially a blight on the rest of my image, which is massive. I dread the idea of having to start from scratch. I can't simply erase it because it doesn't seem to be associated with a layer. Originally, the image was created in 2.6, I think (but am not sure) that this is the version I used to make the line, but when I got a new computer I downloaded 2.8, and after this discovered the problem. Everything else works normally, is responsive,etc
Appreciate any help!
Elia