Call the company's customer-service line-and be civil. Complaining in anger just tells the service rep you're so fed up that you'll never come back anyway. Ask for a supervisor only if you've politely tried and gotten nowhere with the rep first. If you don't get results over the phone, send a letter to the company's top officials (check its Website for names). State how long you've been a customer: Companies do not want to lose their best customers. Then, spell out exactly what happened and how you'd like the situation remedied. Include as much evidence as possible: sales receipts, contracts, ads, guarantees. As a last resort, say you're reporting them to the Better Business Bureau. This threat won't always work, but most organizations know that being on the BBB's "complaint list" can tarnish their reputation — and cost them potential business.