It does not matter if it's a telemarketer or someone you know that annoys you. Sometimes it's best to stop you from calling or using FaceTiming. How to do it on your iPhone and iPad.
iPhone and iPad owners have countless ways to connect, whether it's a phone call, a FaceTime audio call, or a FaceTime video call. Despite the many different ways that someone can contact you, iOS uses an all-or-nothing approach. This means that blocking someone from calling you also prevents them from contacting you through FaceTime. As a practical bonus you can not be reached via SMS or iMessage.
You can prevent contacts in the FaceTime and Phone apps from reaching you. This in turn blocks all contact points, no matter where you are. Do it ̵
Block contacts in the phone application
Open the phone application to get started. Depending on whether you are blocking someone in your contact list or making a call, tap the "Contacts" or "New" button.
Tap the name of the contact when you are in the Contacts tab. Touch the Info button next to the caller you want to block when in the New tab.
Next, scroll to the bottom of the page and tap "Block this caller" option.
Confirm the block by tapping "Block Contact".
Blocking Contacts in the FaceTime App
Blocking a contact in the FaceTime app is similar to the one in the phone app. This time, however, you can only block people who called you or called you earlier. If you're blocking someone else, the phone app is the place to go.
Start the FaceTime app and tap the "About" button next to the name of the person you want to block. 
Now scroll down to the bottom and touch the "Block this Caller" button.
Finally, confirm the implementation of the block by tapping "Block" Contact.