Thank you for reaching out.
I could not find a Network watcher feature for your specific requirement above (apart from the preview feature Vnet Flow logs which you have already mentioned). NSG flow logs is very similar feature which capture IP traffic. NSG flow logs are written to storage accounts. You can export, process, analyze, and visualize NSG flow logs by using tools like Network Watcher traffic analytics, Splunk, Grafana, and Stealthwatch.
Another approach you can try here is to create a Billing Support ticket for this issue. Billing related support is provided to all Azure customers for free. You can follow the documentation here to create a Billing support request (Just replace issue type to Billing).
Hope this helps! Please let me know if you have any additional questions. Thank you!