duplicate columns A and B

[Rojonia]

Suddenly I have two identical columns A and B in my worksheet and cannot figure out what I did or how to go back to where I was or how to remove the duplication. "Remove duplicates" under "data tools" did not work for me (apparently not designed for my case). I cannot select just one of them and delete as both are selected when I click on column heading. Recovering "previous versions" with ShadowExplorer didn't work either ("wrong file extension(??!"). Any ideas would be appreciated.