There's a huge gulf between the service levels for Silver/Gold vs. DM, and also another gulf between Cantonese and English helplines. My wife is Gold and uses the English helpline only, and I am DM using both, and it's like chalk and cheese.

But it sounds like the call centre was behaving like most ordinary call centres. So I'm afraid Daffie is right.

BTW, very few airlines offer a guaranteed seat. Even though CX is going to restrict this benefit to Y tickets only from April, it's still an unusual benefit.