What is the ruling on saying "I implore You" with the intention of pleading, and is this considered major shirk, and what is the ruling on the unlearned person who issued a fatwa to that effect?

The word mentioned is not polytheism (shirk), for it is permissible to ask a living person who is capable of doing something, and it is permissible to seek his help in a way that assists him in doing it. Polytheism is directing worship to other than Allah, and this is not present in the question. Whoever said that must repent to Allah and refrain from issuing fatwas without knowledge, because speaking about Allah without knowledge is one of the gravest major sins.