Recalculate your mobile and broadband plans annually: downgrade unused services, and file a complaint if the carrier refuses to comply

Cost: No expense at all. It takes just a few minutes to review your bill. The real challenge is resisting the pressure from customer service reps who try to dissuade you from downgrading.
In plain terms: Older plans you’re currently on often cost dozens of yuan more per month than newer plans now on sale. Those extra monthly fees add up to hundreds of yuan wasted each year. By regulation, carriers have no valid reason to reject your request to switch plans, delay processing it, or impose special pricing tiers solely for customers making such changes. If they refuse without justification, you can file a formal complaint.
Benefit: Ministry of Industry and Information Technology rules explicitly state that carriers must not “refuse, obstruct, or delay providing number portability services to users without valid reasons”, nor may they “use blocking or restrictive technical measures to compromise the communication service quality of such users”. They are also prohibited from “creating dedicated pricing or marketing plans for customers exercising their right to port their numbers”. Older plans typically cost dozens of yuan more per month than current offerings, so sticking with them results in hundreds of yuan wasted annually.
Evidence grade: A
Sources:工业和信息化部 (2019). 携号转网服务管理规定（工信部信管〔2019〕242 号）. http://www.gov.cn/zhengce/zhengceku/2019-11/13/content_5451483.htm
Notes: First, use your carrier’s official app to check your actual monthly data and call usage over the past six months, then choose a plan matching those figures. If a customer service rep claims “you must visit a physical store to downgrade” or “contract terms prevent any changes”, ask for written proof of those claims. If none is provided, file a complaint via the 12300 hotline.