I do not usually answer questions as forcefully as I will this one but it pushes my buttons. Yes, Catholics are Christians and anyone who told you we aren’t was telling you a lie. All Catholics believe in Christ which is what defines a Christian. But there is more to it.
Catholics are different from all other Christians in that we do not belong to a denomination. All other Christians denominated from Catholicism. The term “catholic” means “universal.” From the very beginning, the Church spread universally. In the Early Church, if you were Christian, you were Catholic. It was that simple. That is all there was.
The Catholic Church was founded by Christ Himself. He made Peter the Rock on which He built the Catholic Church. This Church is apostolic, meaning it has been passed on through unbroken succession for the last 2000+ years.
All other denominations broke off from this one, holy, Catholic and apostolic Church and were founded by a man or woman.
So, yes, Catholic are Christians. I would go as far as to say the original Christians.