Refund dispute

I cancelled an Airbnb booking which they refunded, but only the one payment reflected in my account. I contacted discovery card to find out what to do, they said I should lodge a dispute (Aug 2019), they stated it would take 30 days. Discovery said the dispute was resolved but they referred to the incorrect transaction. I contacted them again and was told to lodge a new dispute (Nov 2019) with the same result, I then asked to talk to a manager who told me to lodge another dispute (Dec 2019) same result again. I call and emailed discovery and asked to speak to a manager but with no luck. They sent an email state a manager would call me on Monday 24 Feb 2020 but they never did. The service has been so bad that I don’t know what else to do.