I'm also running into the same problem. I clicked the link in the email. I pick the mini color. I check out but still see the $49 + tax amount. I checked and I am registered. In the URL it even has the discount code.
Quick update since I am having a similar issue with my order. I did connect with Spotify support and spend probably an hour with them. The support dude was very nice:) and helpful but they did not get back to me.
Since I am a software engineer here is my 5 cents on this issue. This may help people around to understand the issue with canceled orders.
1. Spotify has a single google promotion code locked for every user.
The support chat really is a waste of time, they offered to escalate to a special team which never responds in the time frame they set, this is on multiple occasions. I am very familiar with customer support industry and messaging support as well and their team frankly is a disappointment and the main reason I am no longer a Spotify customer.
I've gone back and forth with support at least 5 times on this issue. They are prompt in responding to me but clealy have no clue as to how to resolve the issue. I did just forward them the post here about the promo code having already been registered and that causing Google's backend to mark the promo as having already been used.
I'll keep you posted on what I hear back.
Re: Google Home Mini Promotion still trying to charge full price?