Topbonus promotion : return of 30% of used miles

I received a promotion email in April about an easter promotion.
For your bookings you would receive up to 30 % of the used miles back: both for upgrades and regular awards.
I registered - and as always with airberlin - I did not get any kind of confirmation email. So i called the Platinum desk and they confirmed the existance of that promotion and my registration.
I then went ahead and booked 2 free tickets EU-US-EU and upgraded another one EU-US-EU.
Now, the deadline was May 31st for recredit. As nothing appeared I called the service desk again (willing to book another trip on those old rates) and they again confirmed the registration for the promo and said that i would take some more time and I should wait another week.
After 10 days I called again. Now they claimed I never registered and they cannot make an exception and I would not get any refund.
So, is there anyone around with the same problem or is it just me? Of course I registered for that promo as I was already looking for flights for 2018 and I am - of course - always looking for ways to get more bank for the buck.

So, what would you do in my place? Is there anything I could do anyway?

Thanks for your support.

I took part in the promo as well, and I only noticed that the promo miles were credited because my overall balance jumped.

They had posted with a weird description way down in my mileage account.

Are you sure you didn't get the miles? Just asking...