Madam Chair, I don't understand your ruling.
First of all, subs are allowed. Secondly, unless this committee has adopted a motion prohibiting substitution, which I doubt has occurred.... If the committee has not adopted a special order to the contrary, the rules permit the participation of members—though they can't vote—if they're duly elected members of the House of Commons and they're present at the committee.
If your understanding of the rules is different, I would invite you to cite the relevant Standing Orders or sections of Procedure and Practice. I am quite certain that members are allowed to speak if they are associate members of the committee, which I am. I'm an associate member of the committee. Associate members are allowed to speak, but they can't vote.