How does Special Counsel John Durham prove Igor Danchenko never received a call from Sergei Millian, when Millian is unavailable at trial?

Easy. Just introduce Danchenko's phone records.

Here is the full document - Durham's opposition to Danchenko's motion to dismiss:

https://www.scribd.com/document/595004262/83-Gov-Opposition-to-Danchenko-Motion-to-Dismiss