IPhone blocks contact on its own

The simple solution is to un-block the number.

Settings > Phone > Call Blocking & Identification

Another possibility is that your cellular service provider blocked those numbers for reasons unknown. You'd have to contact them for assistance.

mmm ... I'm skeptic that your iPhone blocked from his own some of your contact. Anyway ... unlock them Block phone numbers and contacts or filter messages on your iPhone, iPad or iPod Touch - Apple Support and if happens again without your action, well ... contact the Support!