Since he is making the accusation, the burden is upon him. Do you have a catechism?
Ask him why the New Testament is actually called the New Testament. The answer is the Eucharist. The consecration in the upper room is the only place in the scriptures where the words “new testament” are used - and Christ used them. Remember also that it is a commandment of Christ. From the King James Version:
Matthew 26:28
For this is my blood of the new testament, which is shed for many for the remission of sins.
Mark 14:24
And he said unto them, This is my blood of the new testament, which is shed for many.
Luke 22:20
Likewise also the cup after supper, saying, This cup is the new testament in my blood, which is shed for you.
1 Corinthians 11:25
After the same manner also he took the cup, when he had supped, saying, this cup is the new testament in my blood: this do ye, as oft as ye drink it, in remembrance of me.