Why are my emails going from the Inbox to the Trash on Yahoo webmail?

For the last 2 days, emails that show up in the Inbox stay for a few minutes and then move directly to the trash without prompting. This appears to originate from Yahoo webmail. Now the trash folder is deleting automatically. I can't get any support from Yahoo tech support since we have an att.net email not a yahoo.com email. We've changed passwords. I have no filters. Scanned for Malware and viruses. We're a business and not getting our emails is a HUGE problem.