If we do not answer, It is simply because we are busy with customer's at the counter (and it would be rude to stop attending to a customer to take a phone call) or you are using an anonymous or private phone number.
As calls from anonymous and private numbers are tele-marketers, scammers, and general time wasters 98% of the time, we simply do not answer them, as we do not have the spare time to deal with all the tele-marketers etc.
If you are a genuine customer calling from a hidden number, then either leave a message (with your number) or call from a phone that doesn't hide their number.
We do not have an office lady or receptionist for taking calls, hence why we screen out the rubbish calls.