You’re incorrect on both legal and factual grounds. The First Amendment applies only to government actors. Private companies, including Mastercard, have no legal obligation to carry or support speech they disagree with. This is settled law (Manhattan Community Access Corp. v. Halleck, 2019).

Net neutrality was about common carriers (ISPs) due to their chokepoint role in internet access. Payment processors are not classified as common carriers and are not subject to those rules.

If you want laws changed to regulate them like utilities, that’s a policy argument, not a free speech violation under current law.