No refund received when upgrading to game pass ultimate

You would have had to request a refund before purchasing Ultimate. The Game Pass you originally purchased would have been cancelled and upgraded to Ultimate in addition to the Ultimate you purchased.

If it were cancelled automatically once upgraded, should I not then receive a refund automatically?

When you added the Ultimate, the PC Game Pass was cancelled and upgraded to Ultimate. So it was no longer eligible for a refund.

To clarify - That's how it works to upgrade. You still get the full amount of time you paid for the standard Game Pass plus the amount of Ultimate you purchased. So if you bought 1 month of Game Pass and 1 month of Ultimate, you now have 2 months of Ultimate. If you do request a refund, as suggested, you will only receive a refund for Ultimate and will lose all of your subscription.

You don't get a refund or any kind of discount when you upgrade. So it worked correctly. It upgrades it because you've already paid for one subscription and you're getting more for what you paid for. In order get a refund you would have had to cancel Core and request a refund prior to buying Ultimate.

Since you purchased Game Pass Ultimate, the Xbox Game Pass would have been upgraded and the time would have added onto Game Pass Ultimate. So you wont be able to get a refund.