Understanding that your team have the greatest day to day impact on controllable costs is important. After being promoted, if you found [show details]?

Thanks for the invitation.

I will try to make them realize the mistake they are doing and give them a chance to correct. Still if they do not fall in line either I will report to my senior about their actions or I myself take action against them if I am a senior.

It is important to see that company will not suffer due to somebody's willful mistakes.  

You need to analyse the facts and then have a meeting with the staff member. It is always a smart option if the findings warrant it, to have a representative from the HR Department to sit in when you are discussing the issues.

in the first instance, it is always worthwhile to try and resolv the issue as if dealt with too heavily, will impact the team.

The fact that you have identified the failing and willing to discuss it initially will make the staff member aware of the situation and your expectation. I would be surprised if this process did not self correct.

If it does not, then the performance management process should take over. If the staff member is not the right fit, then this process will either realign the member or provide justification for dismissal.

Thanks for invitation -

I will support them with my capabilities as personal as possible  !

you may make them understand by re-iterating the importance and its consequences on team if not followed. thanks.