Normally, you should be able to counter Deadly Dispute if you want, so if you were able to resolve a counter spell but Deadly Dispute still resolved, it means there was an onboard effect or such that made his spell uncounterable. This usually indicated by like red aura around the card while it's on the stack. If we had the screenshot, we could easily point it out.
Don't worry, people aren't trying to be mean, it's just difficult to answer your question without more information. At least you know better for next time. Try to get a screenshot or at least note down what the other onboard cards are.