Hi @Leonasophie, welcome to our Community!
Please be aware that even if your account was ever downgraded, Dropbox wouldn't delete any of your content.
Upgrading the account wouldn't work if the files were deleted a long time ago. When you upgrade your account, the extended recovery time is only effective from that point on. It does not work retroactively.
Have you checked both your deleted files page, and events page for the missing content?
Keep me posted, and we'll take it from there!