Adding VAT account to MTD Gateway account

I was previously registered for VAT and my old account is still showing when I log into the HMRC site. When I click on the link to add a Tax Account, I am able to enter the details of my new VAT registration, however, at the end of the process it tells me that it cannot add the account. I also can't see a way of removing the old VAT account. Can someone point me in the right direction?

Hi Greg,
Please contact our Online Helpdesk team 0300 200 3600.
Thank you.