I think I was charged after cancelling

Cancelling your subscription stops future renewals — it takes effect at the end of the billing period you have already paid for, not the moment you press cancel. That means a charge dated before you cancelled is the normal charge for your final period, not a new renewal.

First, compare the date of the charge with your billing period: if the charge is dated on or before the day you cancelled, it belongs to the period your cancellation closes out.

If the charge happened after your cancellation took effect, something has gone wrong and we want to fix it. Email support@barcodesqr.com with the transaction details — the date, the amount, and your account email — and we will review it right away.