Hey @mark_fisher70 you might have logged in to a different account.
Please log out from the current account and login again with the email and corresponding password linked to the account with all your music.
If the problem persists, please let me know. 

Sounds like the app updated overnight. Was your music downloaded to an SD card? This happens to me regularly because of a bug in the installer that's existed for months.  I've disabled automatic updates as a result since it's no fun taking the dog for a walk and finding out 100GB of downloaded music is gone. I only update the app now when I know I've got time to redownload everything. 

I logged onto my account today & the same thing happened to me - absoloutley everything had gone - years of all my favourites and downloads. Not happy. 

What was the solution ? 

Hello @esther parkinson you might be in the wrong account as I can see that you created a new account rather than logging in to your usual account.
Please log out and login again with the email and password for your Deezer account.
If the problem persists, please contact our Deezer Support Team and provide the email and user ID of your Deezer account and one of our agents will be able to help.
Thanks :)

Many thanks for your help. This has now worked