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Hi Pierre,
What precise resource types did you create in your subscription? From your description it sounds like you created a resource (or multiple) and it has been accruing charges ever since. There are definitely resources that you can create that cost $394 or even a lot more each day.
To stop accruing charges I recommend backing up any data (if any exists you need to keep) and then deleting the resource(s) immediately. Often it is easiest to delete the resource group which contains the resources.
If you navigate to your subscription in the Azure portal, next on left click on Cost Management -- Cost analysis, then at the top click View -- Cost by resource. This will show you a breakdown of costs by each resource, with the highest cost item listed at the top.
If you have any questions or are unsure please add a comment below. It is important for you to get the resources that are accruing charges deleted to stop future costs.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP