@Will235 . First off, I am so sorry to hear that you have heard a cancer diagnosis. I can only hope that your treatment will be successful, and you will never need to hear those words again.
Clearly, AirBNB didn't think an email was sufficient. If you spoke with a customer service person in the US, they would consider an email to be unusual. Our privacy laws dictate that doctors do not use unencrypted email but instead employ server based message systems. A friend, who faced a similar diagnosis, submitted her biopsy report along with a report that outlined her treatment protocol. AirBNB helped relocate all of her guests and there was no charge. She was able to retain her SuperHost status as well.
If you have the energy, you might want to call AirBNB once again and ask for a reconsideration after submitting more suitable documentation.
All the best to you during your treatments. I hope that you have a community that can surround you with love and support.