Praise be to Allah.
If the debtor is given zakaah for the purpose of paying off his debt, he should not spend it on anything other than his debts, because it was only given to him for the purpose of paying off his debt, not to take possession of it himself.
Al-Bahooti said in Kashshaaf al-Qinaa‘ (2/283): If money is given to the debtor with which to pay off his debt, it is not permissible for him to spend it on any other purpose, even if he is poor, because he only received it for a specific purpose. End quote.
That is, he received it for a specific reason, which is to pay off his debt, so he should not spend it on anything else.
And Allah knows best.