The amount taken from your card when your subscription renews can be higher than what you paid the first time if tax rates in your area change or if you move somewhere with higher tax. Because Wordwall says a tax change is not a price change, you may not get the warning or the right to object that you would normally expect before a price goes up. Prices shown on the site also no longer include tax, so the checkout total may be more than the advertised figure.
“A change in tax is not a change to the price.”
What you can do — Before your next renewal date, check your account or last invoice to see the actual tax-inclusive total, and cancel before the renewal if the new total is more than you want to pay.