How do I protest a credit score policy that unfairly lowered my score for taking an offer for a new credit card with0% interest for 15 months?

[Opus 17]

Opening a new line of credit, and having a “hard inquiry” on your file (usually part of opening a new line of credit) will both temporarily lower your score. That’s how the scoring models work, and if you did open a new line of credit, that will be reflected in your score for a while.