hummingbird....we all have different styles....My way, with this kind of request, would be short and to the point. "No, I am not going to enable you".
If he wanted to debate and argue with you about it....I would say "This is not negotiable". "Sorry".
If he pushed on and threw a tantrum....I would simply say, "Call me later, when you are in a better mood...goodbye".
He sounds at about 14yrs. old, in terms of his assuming adult responsibilities....so, I think you may have to respond to him the way a parent presents boundaries for a 14yr.old. It is not mean to do so...it is being a good parent, in my opinion. He is going to need to mature and grow up, emotionally....
Here is an underlying principle----the young adult struggles with the developmental task of independence/dependence....Nature is pushing them in the direction of wanting independence...yet, they are still dependent in some ways....inside, they hate still feeling dependent....so they transfer that "hate" onto the parent......At the same time they are asking you for stuff---they resent you for being there to give it. You remind them of their dependence.
There is generally conflict between the parent and the young adult, at this stage.....If all goes as Nature intended...both parent and child stumble and grow through it all...…
but, if something(s) interfere with this developmental stage...some people stay stuck in it.....
Remind yourself....
No enabling
No JADING for you
No false Guilt!