I assume you’ve done the standard thing, right. Picked one item of doctrine they disagree with you on and then said, “Hey, let’s settle this the way Christ instructed us to.”
That is first you try to correct them. Then you have a couple of witnesses (your catholic friends) try to correct them. If they refuse to listen to you, then go to the Church. If they refuse to listen to the Church- treat them as an ancient Jew would have treated a tax collector.
Matthew, 18; 15-18
'If your brother sins, go and tell him his fault between you and him alone. If he listens to you, you have won over your brother. If he does not listen, take one or two others along with you, so that every fact may be established on the testimony of two or three witnesses. If he refuses to listen, tell the Church. If he refuses to listen even to the Church, then treat him as you would a gentile or tax collector. Amen, I say to you, whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.
Problem your protestant friend will have is-- what church do you go to in order to settle it? Christ obviously intended there to be a real, physical Church with the authority to settle disputes on earth. Your protestant friend can’t tell you to go to his church because, why his protestant denomination vice the hundreds of others? Especially if their interpretations and teachings have changed over time. And each congregations minister has different interpretations. You have to figure out which one is the one true Church, a Church which has taught consistently and has actually recorded it’s doctrines—Welcome my brother to the Catholic Church established by Christ to settle these disputes via it’s authority to teach infallibly, Christ would not commit himself to binding or loosing things in heaven based on fallible decisions on earth.