The Epoch Times is not exactly a reputable source, but that doesn't mean user counts haven't decreased. E.g. China Telecom's numbers show a drop of 5.6 million users in February: https://www.chinatelecom-h.com/en/ir/kpi.php?year=2020

I think it's unlikely that anyone who died remembered to cancel their contract beforehand and I'm not sure how quickly the Chinese bureaucracy would issue their relatives death certificates. The people who cancelled are probably alive but need to save money.