Although people pin a lot on her (and she isn’t 100% blameless), I think this exercise was supposed to be a hit at his father because Prince Charles quit giving them an allowance.
I bet his father “quit taking his calls” because there was nothing more to discuss on the subject and any other conversation would devolve into trying to get the money payments back.
I listened to that part of the interview again, and I believe what Harry said was that his father stopped taking his calls during Megxit time, but now does take his calls.