Hi Pjsmith
Sorry to hear you've been having issues with your BTinternet email - if your email ends with @ btinternet.com then this is a residental email. Do you pay to keep this email address (aka Premium Mail who are dealt with by 0808 100 6778) or do you have it linked to a BT Residential account?
Either way, BT Business can not assist with @ btinternet.com email addresses so it would need to go to Premium Mail if you pay for it, or the Residential team if you do not.
Beth