Hi,
You can look at the usage details to see precisely which resources you are being charged for on the invoice. In the portal, navigate to your invoices, to the right of your invoice click the context menu (three dots) and choose Prepare Azure usage file.
There will be a delay while the file is being prepared. Once it is ready you can download it from the notification. After downloading it to your computer you can open it with Excel, Sheets, etc., and do a find for "Managed Disks" until you find the specific line(s) for the E4 LRS charge. On that line, it will have the full details such as resource group, name of the disk, location, date, subscription id, etc. Using this file you can see if it only existed for part of the month or all of the days and often you can tell which VM it was associated with based on the name.
Please click Accept Answer if above was useful. If something is unclear, add a comment below.
Thanks.
-TP