Some legal presumptions cannot be argued against in court. Once a conclusive presumption applies to your case, it is treated as settled fact no matter what evidence you might have to the contrary.
For example, if a law says a certain fact must be assumed true under specific conditions, no one can bring evidence to disprove it. The court will not even consider arguments against it. This is different from other presumptions that can be challenged with the right evidence.
If a conclusive presumption applies to your situation, you need to understand that fighting it is not an option in court. Your best move is to talk to a lawyer about whether the presumption actually applies to your case in the first place.