user name for @mac.com is incorrect

I'm getting a message on my iphone

'the username or password is incorrect'

it had been working fine. I did have an old user name and password and have since created a new one, as I for got old

password. email has been working fine. My husband and I both have the same accounts with both of our iphones. He just

went overseas and since then we have been getting this message. not sure what to do.