Hi,
They recently changed Developer level support plan so that it provides priority response from Support engineers on Q & A within 8 business hours instead of support via email/phone. This is the reason why you are unable to create a support ticket as you did previously.
Standard level still provides support via email/phone, but costs more.
https://azure.microsoft.com/en-us/support/plans
Below article is for Microsoft for Startups Founders Hub members, but it is applicable to Azure Developer level support plan as well:
Priority Community Support with Microsoft Q&A
https://learn.microsoft.com/en-us/microsoft-for-startups/priority-community-support
NOTE: Billing or Subscription management or Service and subscription limits (quotas) support requests are free of charge and can still be submitted via Azure portal, regardless of which support plan you have.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP