I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to accept the answer.
Solution:
I finally managed to get this sorted, My account was already a MCA.
In the end I logged a support ticket in the Azure portal (Help + support). Even though my query was about new subscriptions I had to log this under an existing subscription which allowed me to log a ticket. Im now able to create more subscriptions.
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