Appointment and Signature Required Deliveries – How do you deal with unresponsive customers?

We do quite a few big and bulky shipments to Amazon customers, stuff like sofas and outdoor furniture, so all our deliveries are both signature and appointment required. We dispatch our own trucks and these are not FBA orders, and oftentimes our truckers say that customers don’t respond to voicemails to schedule deliveries. I think it’s because customers ignore calls from numbers they don’t recognize and I don’t blame them, but does anyone else experience this and if so, how do you work around it?

TIA.