Section 60E(2A) of the Employment Act may give you some info:
"(2A) Notwithstanding subsection (2), upon the termination of an employee's contract of service, the employee shall be entitled to take before such termination takes place the paid annual leave due to be taken in the year in which the termination takes place in respect of the twelve months of service preceding the year in which the termination takes place, and, in addition, the leave accrued in respect of the completed months of service during the year in which the termination takes place."
So, you should have applied for the 18 days annual leave balance before you go and let management approve it. If you had done that, you might not have this problem.
You see, your notice should be from 28 Oct to 27 Nov (31 days), but you left on 6 Nov which is 22 short. If you were to use your 18 days annual leave to pay for the short notice, you still need to top up with another 4 days' salary. This is just another view. Consult the Labour Department for an official opinion.