I installed the update to 6.2 as recommend, now writer docs show as OST and won't open?

Deleted the download because I thought it had uploaded. Today find that what were otd now show as ODT and I can’t open these writer documents. To complicate things further because I had no download file to repair with, I have downloaded a version7. I still can’t open writer documents. Any help gratefully received!

Which operating system do you use?

Is the problem that the extensions is written in all UpperCase and your System does not open them with LibreOffice?