Yahoo Mail Vanishing Contacts

I have been using Yahoo Classic (?) mail via the Chrome browser on my W7 PC for years and have not yet upgraded to the latest mail version in spite of prompts. Suddenly all my "contacts" have now disappeared, none can be seen or retrieved. If I "edit" the name of a contact from an email he has sent me the system won't allow me to "save" it. Likewise if I try to "create" a new contact, when I hover over the save button, the "no entry" circle appears. There does not appear to be a button visible for "retrieving" contacts.
Is this a bug that has targeted me solely or have other Yahoo Mail had the same problem? Is it recognized by Yahoo (somewhere) and most importantly what is the cure??!! Tks