I'm sorry to hear that you are having problems with SDFCU. If this had happened to me, I would be calling their fraud department to find out exactly happened. I'm sure there is a logical explanation for this. The credit union is required by law to explain why your accounts were closed. One thing I have noticed with this credit union is you have to speak to the right department(like fraud or Lending Solutions), the regular CSRs in the call centers are very limited with info.
I'm a US born citizen with a foreign name as my father immigrated here many years ago. I had no problems joining at all. When I opened my checking and savings accounts, the credit union did a soft pull. They also did a hard pull when I opened my credit card. The only documents I had to email them was a copy of my driver's license, pay checks, and signature cards.
Please let us know why SDFCU closed your accounts when you get the notification in the mail.