ChloeCurious Did you change the email address or password associated with your EA account? Does either one contain special characters? You might need to remove those. And even if there aren't any special characters, changing the email or password can break things temporarily.
Aside from that, please remove the file labeled [your email].bin inside Documents > Electronic Arts > The Sims 3 > Downloads. In addition, clear Edge's Internet Explorer-mode data (Windows) or Safari's cache and cookies (macOS). And let me know what platform you're using if this doesn't help.