A MX for domain already exists

Hi

I decided to buy new domain (domain2) without hosting and to have e-mails from it i decided to buy MXPLAN 5
Now i decided to buy hosting2 connected to domain2. I expected, that during the process the MXPLAN5 would be upgraded to MXPLAN 10 hosting and connected to the server, but that didn't happen.
Now when checking the hosting2 i see the mail is inactive. When trying to activate it and selecting domain2 it gives out an error "Cant activate e-mail: Order not possible. A MX for 'domain2' already exists."

So iI' unsure what to do next. I expect that removing MX records from DNS wont be enough and I'm not really want to try on cancelling/disabling MXplan5 to see if that would free up activation of mail.