Mails that can't be opened in Yahoo
 

Recently, I have received several e-mails which I could not open.
When I tried to open them, I got the message "we did not understand your request". I wrote to Yahoo and predictably they did not respond.
One of these e-mails that could not open mysteriously disappeared. I did not delete it. It is not in my trash. Just gone. I have another one now that's a very important e-mail. Every day I try to open it and everyday I get the same message that they do not understand my request.
Does anyone have any advice about this?
Do you know if paying customers (for example, Yahoo plus people) get better customer support?
Thanks for any help you can provide!