Strange bill changes linked to a phone plan

Lately a mobile bill started to climb even though call habits stayed nearly the same and no one in the family remembers adjusting the plan. Extra line items showed up with short labels that do not clearly explain what kind of service they represent. Since several people share the account, it becomes tricky to figure out whether someone agreed to a new feature during a store visit or if a system change added it during an update. Worrying about every call or text takes the fun out of regular communication. How can this kind of situation be reviewed in a calm, structured way so that any optional features can be identified and either kept or removed without turning the issue into a long argument?