And if a coworker is refusing to speak with you on the system that the company provides you to speak with them, why haven't you complained to your manager (or your manager's manager) about the clear and obvious blocker to getting your work done?

One of the following is true: OP is the biggest doormat in the world, the company OP works for is incredibly dysfunctional and cannot be saved, or OP's story could be found in the "Things That Never Happened" Jeopardy category.