If the amount charged is higher than the price shown on the pricing page, this is usually because of local taxes.
When changing plans, the modal also notes that prices are exclusive of local taxes. Your actual charge will include applicable tax.
One-off credit top-ups also show "plus any applicable local taxes" at checkout.
Check your actual charged amount and receipt in Manage subscription → Payments table. If the amount still does not match what you expected, contact us via the feedback form with your receipt.