Late payment- moderate tone: final notice

I am following the previous three letters we sent to you with this final letter, hoping that we will not be forced to forward your account to a collection agency. Your account has been unpaid in the amount of $[AMOUNT] for over four months. Reluctantly, if we do not receive payment within the next five business days, we are left with no alternative but to take actions which may permanently and adversely affect your good credit rating. Indeed, it would be to both our benefits to resolve this matter immediately. Again, we hope to receive your payment within the next five business days. Sincerely,