<SectionList
                renderItem={({item, index}) => {
                  Alert.alert(index); // here the index is null
                  return (
                    <SectionListItem  item={item} index={index} parentSectionList={this}>
                    </SectionListItem>);
                }}
                sections={this.state.contacts.sort((a, b) => a.title < b.title ? -1 : 1)}
              />

removeItem = (deletedKey) => {
    this.setState({
     deletedRowKey : deletedKey,
     // here I want to remove my item with deletedKey = index, but deletedKey is null
     contacts: this.state.contacts.splice(1), // works, removing the 1st item from array
    });
  }

const newContact = {
      title: this.state.contactName.charAt(0),
      data: [{
        name: this.state.contactName,
        phone: this.state.contactPhone
        }]};