Azure OpenAI deployments rejected with error 715-123420 ("unusual activity") on a sponsored subscription, then billing account disabled for "UnusualActivity"

Hello,The Azure support team suggested that I ask the community for help. I have open support cases, but I am on the Developer support plan and the issue is not resolved.SetupA Microsoft Customer Agreement (MCA) billing account; the subscription offer shows quotaId: Sponsored_2016-01-01.A small company (healthcare software) running Container Apps, VMs, PostgreSQL Flexible Server and an Azure AI Services resource, in Sweden Central and South Africa North.Problem 1: every model deployment is rejected (since late October)On the main subscription, Microsoft.CognitiveServices/accounts/deployments/write always fails with error 715-123420 ("unusual activity"), even for models where quota is available (for example gpt-5.4-mini DataZoneStandard, with a quota of 1,000).The quota for newer models (gpt-5.5 / GPT-6 family) is 0 in all regions.Not a single AI deployment has succeeded on this subscription since the resource was created.With the same steps on another subscription (same offer type, different tenant), gpt-4o-mini GlobalStandard and gpt-5.4-mini DataZoneStandard deploy without any error. The block therefore seems tied to this specific subscription or billing account, not to the region or the model.On a new subscription created under the same billing account, gpt-5.4-mini DataZoneStandard deploys, but gpt-5.5 GlobalStandard returns InsufficientQuota (quota 0).Problem 2: Container Apps environment quotaMaxNumberOfGlobalEnvironmentsInSubExceeded: the subscription is limited to 2 managed environments. The automatic quota request (ManagedEnvironmentCount, South Africa North) fails, so I opened a support case to ask for 2 more environments.Problem 3 (most urgent): billing account disabled for "UnusualActivity"A few days after these cases, the billing account was disabled with the reason UnusualActivity. The subscription is now in the Warned state (read-only), and all running workloads (Container Apps, VMs) stopped.No spending limit is involved (it is off), and no credit is exhausted.A related detail: the sponsorship credit balance does not seem to go down, even though there is real usage on Cost Management (a few hundred euros this month).What I have already doneOpened support cases (AI deployment block, Container Apps quota). I answered every question from the engineers with the Activity Log entries (failed deployments/write operations with correlation IDs), the offer details and test results.I cannot create or update cases through the Support API (InvalidSupportPlan on the Developer plan), so everything goes through the portal.QuestionsWhat does error 715-123420 mean exactly, and which team can review and lift it (fraud/risk review, Azure OpenAI access, billing)?How should a billing account disabled for UnusualActivity be escalated, and is there an identity or company verification process to reactivate it?Is there a known issue with Sponsored_2016-01-01 offers (model deployments blocked, quota 0, credits not consumed)? Should we move to a different offer, such as a standard pay-as-you-go MCA?Will a new subscription under the same billing account inherit the same restrictions?I can share the case numbers, subscription ID and correlation IDs privately with a Microsoft moderator.Thank you for your help.