1: Are you sure you are using the correct google+ account?
2: When entering your e-mail have you made absolutely sure that it is 100% correct? Because depending on your bluestacks version and keyboard setting (which after uninstalling and reinstalling a new version might have been scrambled) sometimes after typing the @ the next letter will not appear and it will tell you, that there is no account.
3: In the case you have tied it to facebook, have you tried connecting it with facebook?
4: Farfetched but bluestacks is an android emulator, are you 100% sure bluestacks 3 still emulates android?
5: If this doesn't work, send old screenshots from your account id to the support.
6: Incase you don't have your account ID, goodluck with real life!