How to Not Accept Blocked Calls on Your iPhone
A "Blocked" caller is usually one who has hidden his phone number from your view so that you will answer the phone not knowing who the caller is. This can be frustrating from the recipient's point of view, because many annoying telemarketers and others call from blocked numbers, forcing you to answer their calls to find out who the caller is. Although there are no easy ways to prevent this from happening, there are ways to make it less annoying.
Press the "Ignore" button your cell phone or iPhone when the phone rings and it is a blocked caller. If using the iPhone, you'll have to slide the cursor to the right and tap "Ignore."
Contact your cell phone provider and advise the provider of the blocked caller, if the calls continue. You may have to consider changing your phone number if the calls become a nuisance, but generally, they will stop after a few times not answering the phone call.
Try to save the number and assign a ring tone to it so you know it is the blocked caller by the ring tone that's playing. Depending on the phone, you may be able to assign a vibrate mode to it instead of a ring tone.
Answer the phone if none of the above are options. If it is a telemarketer, ask him to take your phone number off his call list. He should remove it immediately and you should not receive any more calls from him.