The only interpretation of Moses that Jesus offers is that he allowed divorce, contrary to how it was at the beginning, because of the hardness of hearts of the people.

Matthew’s Jesus then says “I however say … ” ie he is knowingly giving an opposing command. An unthinkable statement by Shammai or Hillel.

You’re confusing “arriving at the same teaching” with “having the same interpretation”. Shammai’s teaching is his interpretation of Moses. Matthew’s Jesus’ teaching is his own, it is said to oppose Moses.

Here’s how the conversation did not go in Matthew:

Pharisees “Is it right to divorce for any reason?”

Jesus “No”

Pharisees “Why then did Moses command us to give a certificate of divorce”

Jesus “Moses only intended these certificates to be issued in the case of infidelity, and I reiterate this command of Moses”.

Robert said
You cannot show how the Matthean Jesus’ interpretation of Moses disagrees with that of Shammai. Where is the difference?? 

The Matthean Jesus’ interpretation of Moses is that divorce is permissible for any reason.

Here’s the Pharisees question restated.

“If it is not the case that divorce is permissible for any reason why then did Moses command that a bill of divorce be issued send her away?”

In order for Jesus to agree with Shammai’s interpretation his response to the Pharisees must be, “these certificates were only permissible in the case of forbidden sexual intercourse. However his response is “Moses permitted you to divorce your wives owing to the hardness of your hearts” – with no hint of any limitations on this permission.

The limitations on divorce are, according to Matthew, entirely due to Jesus “I however say … “.

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Also Matthew 5:18 “For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished.” 

That is, no-one, not Jesus nor Moses can change the law. It is immutable for all time.

Matthew 19:8 “Jesus replied, Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning.“

That is, Moses’ permission contradicts what was there from the beginning – therefore it can’t be the true law.

It doesn’t need to be restated, that was just for clarity. The point about Jesus’ response still stands. He must say “these certificates were only permissible in the case of forbidden sexual intercourse” in order for his interpretation to match Shammai’s.

However his response is “Moses permitted you to divorce your wives owing to the hardness of your hearts” – with no hint of any limitations on this permission.

The limitations on divorce are, according to Matthew, entirely due to Jesus “I however say … “.