i synced my ankiards on my macbook before erasing it but when i logged in again my account had been set to default and all my cards dissapeared
You can recover your collection from an automatic backup:
I tried this. it did not work.
Can you please provide more details? Otherwise, is really difficult trying to figure out what your problem could be:
I’m afraid there are no cards in your AnkiWeb backups, which means you may have accidentally synced in the wrong direction and not noticed. Unfortunately you will not be able to recover your data unless you can locate a backup on one of your devices.