Not sure if this is relevant for you, but I had a similar problem with my BT email account earlier this year. I forgot my password and had to change it and I was having the new pass word rejected every day and having to change it again. Finally worked out that my tablet still held the old password and that was causing the rejections. Now I consider myself fairly computer literate, but I could not work out how to change it on the tablet. I ended up disallowing access on my tablet to the email search and only now go into the emails on my PC.
And technology is supposed to make life easier for us!!