Do not use favour in the sense that has been discredited by being overdone in commercialese:
Re your esteemed favour of the 24th ult.
Your account is enclosed for favour of your kind attention.
The insertion of favour is no doubt prompted by politeness, and to that extent is praiseworthy. But it is a perfunctory sort of politeness at best, and "for favour of your kind attention" is all padding anyway. There is no reason to explain why an account of money owing is enclosed. We all know only too well.