Correct things to do when leaving Rotterdam

Hello,
I'm just looking for some advice as to what the correct things are to do when leaving residency in Rotterdam?Hello,
May I ask advice please??

I moved with my son exactly a year ago he came to study here at the age of 16, so I basically came as guardian and for support.
We have our residency passes etc and service numbers.
He has lived here permanently I have live here part time, of the 12 months, I have been here for 7 of the 12 months, for five months i have been working in other EU countries.
I also have maintained my tax and national insurance liabilities to the UK.

It's been a mixed year ,but we leave Rotterdam during August 2014.

I will return to work in the uk for the next 3 months,he moves to Maastricht for uni.

What is the correct procedure when we leave the city??

Also I have just received a letter this week from the centraal justitieel incassobureau from the zorginstituut?????? 
Thanks in advance 






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