Can a person still receive my calls and messages if they have blocked me?

You cannot know for sure, but so far everything that you have told us indicates that you have likely been blocked.

There is no way you will be able to tell on your device if someone else has blocked you. A call going to voice mail may simply mean they did not answer your call, out of network range, Do Not Disturb is on, or phone is off. A message not showing Delivered happens for many reasons including:

• Recipient does not have an internet connection
• Recipient phone could be off
• Recipient phone may be on Do Not Disturb
• Recipient may be logged out of their Apple ID
• Recipient may have turned off iMessage
• Could also be a network error on your device.
• Bugs with iMessage that resulted in failure to see the Delivered message has been resolved by toggling iMessage on/off on both devices.

Stop calling them. Or stop harassing them, as somebody receiving unwanted messages might consider it.