If I click on sellers email once having won an auction My old email is the only option I have Even though my new email works as sign in

Hi, Re email address I have changed the email address on my account . It works to log in BUT whenever I try to email a seller to arrange payment it only gives the old , now obsolete address and won't allow change . This means that the seller may be trying to email me and I don't receive it . I have rung to sort this out but all they did was confirm the new email was attached to my account. Please help. Paula