Adobe is scamming me

I signed up for the free trial version of Adobe Acrobat PDF Reader about a week ago and immediately canceled the plan, as my sole intention was to sign a single document. However, it appears that the cancellation was not processed, and I am now being improperly charged on my credit card (which doesn’t even have the available limit to make the purchase in the first place). To make matters worse, I’m unable to cancel the subscription without changing the payment method to a valid card. To my surprise, there are perhaps dozens of identical complaints on Reclame Aqui just in the past week, so I suspect there may be some technical issue at play here. I’d like to reiterate that I canceled the subscription at the moment I activated the free trial and I will absolutely not accept being scammed like this.