Xbox Live (now Xbox Game Pass Core) doesn't "forget" to cancel—auto-renewal is enabled by default on every subscription. If you've been charged unexpectedly, it's almost always due to one of these reasons:
Microsoft's refund policy allows requests within 14 days of renewal if you haven't used the service. Visit Xbox Billing Support and request a refund. Be polite but firm—mention you disabled auto-renew but it processed anyway.
Microsoft has improved subscription transparency over the years, but user vigilance remains essential. Treat subscription management like any recurring bill.