For maximum disruption, phone, then email. If they don't respond in a timely manner (or it's boilerplate bs), another phone call to "clarify" things.
Just remember, the grunts on the phone aren't your enemy. Your goal is to maximise the amount of time you swallow, not to upset them. They could often be allies in hiding.
We don't have to truly break them. We just have to be more annoying than the religious nutjobs.