Problem with KPN Promotion Code

[ThePsYkOKinG]

I recently got a code to redeem 12 months of free Spotify Premium via the kpn website as part of a new internet & phone provider deal.

The problem is that I can only activate this code if my Spotify account is not already Premium.

However I am Premium and I can't cancel the supscription because I bought Premium with retail gift cards.. and I can't wait for my subscription to expire either, because the kpn promotion code is only valid for a few more weeks..

So, my question is: Can you cancel the remaining month of Premium that I currently still have? Or can you alternatively activate the kpn promotion code manually now before it expires?