PK XD 3-Day Free Subscription Asking for Payment

I play PK XD through Google Play and recently faced a problem with the “3‑day free subscription” that is supposed to give discounts and free gifts. The first time I used the free 3‑day subscription it worked, but after I tried it once, the game started to ask me for real money when I want to use it again. A message appears asking for payment and saying that my balance is not sufficient, and it also gives me an option to “restore subscription”, which I do not understand, because the offer is supposed to be free for three days. This problem started around four weeks ago, when a negative sign appeared next to my gems balance, and since then the free subscription no longer works as free and always asks for money. I request that the PK XD team fix this issue by making the 3‑day trial work as a truly free offer again for me and by correcting the negative balance next to my gems, and that they clearly explain why I am being asked to pay money for something presented as a free subscription.