Should I wait to pay?

I had an ER visit January 4, still haven’t gotten the bill. My deductible is $2000. I am assuming the ER visit will put me close to that. However, I also have 2 other really expensive medical appointments next week. My ER bill still hasn’t hit so it’s saying I have not met my deductible yet and each appointment (since they are ultrasounds) are going to be around $600 each. Once I hit my deductible, these appointments are free but as of now they are saying they are $600 (even though I presumably already hit the $2000). Should I told off paying the $600 until after my ER bill or how does it work? What if my ER bill doesn’t come for months? I have united healthcare if that makes a difference.