Use the official support channel
Begin with the business website, app, receipt or published contact details. Social media can be useful for routing, but do not post account details publicly.
Give one complete summary
Include the date, product or service, the issue, what you have tried and the resolution you want. A single coherent message is easier to action than a chain of fragments.
Record each response
Save dates, names or case numbers privately. After a phone call, write a short note of what was agreed.
Escalate proportionately
If frontline support cannot help, ask for a supervisor or formal complaints team. For unresolved consumer matters, the relevant regulator or ombudsman may be the next step.