I cannot reinstall my btinternet email account in Mail...

It all started with Mail not being able to get new mail (but I could still send) last Thursday. I spent days fiddling with the stuff, always ending with "unable to verify account name or password" (but it worked fine on webmail). I contacted the Apple support service who led me through deleting my account and trying to reinstall it but when that failed, I was told that it was a btinternet issue. I then had three completely unhelpful chats with BT including one who put me in touch with a "tech expert" whose first remark was that I was going to have to pay £30 if I wanted any assistance... Am I the only one?? I searched all the discussions and tried reinstalling, etc. I am also NOT particularly computer savvy. If anyone has a creative idea and the patience to lead me through the steps, I will be VERY glad to hear and FOR EVER grateful!!

Thanks!