I'm beginning to think that your problem lies 'at the other end'. (i.e. with your ISP). See below.
However I suggest starting by deleting your account details and re-entering them. Go to Tools > Accounts > Mail. If necessary, click on the name of your account, to highlight it. Then click on 'Remove' and 'Yes'. Next, click on Add > Mail and create the account again, carefully following the instructions here:
https://account.mypos...method=emailSetup#1.1
If you still can't access your account, the problem is almost certainly with the ISP. I've previously had to get two different ISPs to sort out problems ('at their end') in relation to my email access. They both initially refused to accept that it wasn't me that had made an error, but (after a lot of hassle from me) they managed to put things right. I've also had to go through the same arguments on behalf of an elderly friend, whose ISP initially refused to accept that I'd checked her Outlook Express settings with the greatest of care.
Chris