Multiple EKG's

A patient in-patient Hospital received multiple EKG's; two on 9/1/13, 2 on 9/2/13, 2 on 9/3/13. All are read on 9/3/13. All 6 93010 were billed on 9/3/13. 4 have denied as duplicate. I argued that they should be billed on date service done, and supervisor response is: They are billed on date read because that is the date the work was done.

Can you tell me what is the correct date to use?

Thank you