www.labcorp.com billing department address phone number

I wanted to do payments online for my labcorp account however, when i go to www.labcorp.com/billing, it says Please provide your Invoice Number and Zip Code to continue. An invoice number from your bill is required to make online payments or update your billing information. I don't have my invoice number i probably lost it. How can labcorp help me with this? is there labcorp billing department address or phone number where i can check?