This is a tough dispute, because they had all type of equipment to check outgoing calls.

As the call had time stamp, have you checked your phone and app to see what you were doing at the time?

That is a bit strange. You should not be charged data usage for a call. What number does it show on your bill?

Can you provide a screenshot of your bill with a detailed list of charges? Make sure to remove any personal details, as this is a public forum.