How to Navigate between Spreadsheets on O SX

If 2 or more spreadsheets are open I would like to be able to quickly navigate between them. After extensive research on Google and the Tools>Customize>Keyboard menu I tried the existing shortcuts and all any other suggestions I found on Google.

Eventually I decided to delete the existing short cuts (Navigate To Next Sheet and Navigate To Previous Sheet), and to create my own customized shortcuts to see if this would work. I saved my new shortcuts and loaded loaded them but still when I have 2 or more spreadsheets open I am unable to switch between them; the cursor stays stubbornly fixed in whichever worksheet it is in.

Any suggestions will be greatly appreciated - thanks

(Cmd+PgUp & Cmd+PgDn are the defaults. I looked for them after seeing this question)