I need to contact the customer service to erase all my data in the stolen iPhone

I can understand why you may be nervous, but according to Use the Find My app to locate a missing device or item, when you...

Mark as Lost

When you mark your device as lost, you remotely lock it with a passcode, keeping your information secure. This also disables Apple Pay on the missing device. And you can display a custom message with your contact information on the missing device. 

What happens if you erase a device

When you erase your device, all of your information (including credit, debit, or prepaid cards for Apple Pay) is deleted from the device.

assmi wrote:

I need to contact the customer service to erase all my data in the stolen phone.

You don't need customer service to erase all of your data, you can do that yourself by using the steps listed in If your iPhone, iPad, or iPod touch is lost or stolen.

Yes, as long as you complied with the steps listed in If your iPhone, iPad, or iPod touch is lost or stolen.