I have had the exact same experience . They told me to start a ticket. I did. Then they wanted FTP access and an admin account. I complied. They have been putting me off since then.
This is not good customer service.
This addon had a rough history . At first, when Bamastangguy made it, it worked nicely . Then, he made some changes , and it generated an error. I complained, and he became very verbally abusive on here. He refused to send me the original version that worked. Next thing I know, it belongs to Theme House and doesn't work with Xenforo mail, only works with outside mailing services that charge money.
What needs to be done is it needs to generate HTML as before, for those of us willing to wait while Xenforo sends out the emails to our members. it would be great if a scheduler function could be added to schedule the sending of newsletters every month or week.