You haven't stolen from them. The amount in question is not even enough to pay the salary of the recovery guys or the 'chai pani' of police.
The first tactic used by recovery guys is a polite phonecall to recover the equipment and in most cases, the outstanding dues are waived off even when the consumer is actually withholding and it is not true in your case.
If it makes you feel any better, Just send an email to the concerned department in PTCL and put your mind at ease after that.