SU office asks for SU back based on misleading information

Hello to everyone! Thank you for joining me!

I'll make this short: 

I started working in Denmark in February and applied for SU then, starting in the month of March. In my contract it says "40 hours", which was a constant - my hours didn't change, they were always 40.

I was granted SU for the months of March, April, May and June on the basis of this contract only. Therefore: 40 hours = eligible for SU.

So far so good.

Based on the information that 40 hrs in enough (this happens over an year ago), I proceeded to work exactly 40 hours in October and November.

A month ago, the SU office contacted me and asked for the money for October and November back. Their explanation: the months consist of 4 weeks and a half, so 40 hours are not enough.

Let's go back here. 

March: 4 weeks and 3 days
April: 4 weeks and 2 days
May: 4 weeks and 3 days
June: 4 weeks and 2 days
 
October: 4 weeks and 3 days
November: 4 weeks and 2 days.
 
See why I am making this petition now? I will attach it along with my official complaint, because they cannot keep going away with this. I need your names and I need your help, so that for once they cannot escape the consequences for their negligence. Another girl was asked wrongfully to return over 60 000 DKK back, and after filing an official claim against the decision, they told her they made a mistake.
 
Help me do the same!
Thank you for reading!