The most effective complainants are those who have a clear idea of what they want to achieve from their complaint, and who set it out clearly to the person to whom they are complaining.
If you want a refund, for a product or service that didn't live up to your expectations, say so. If a refund won’t be enough, say that too. If you are simply looking for an apology, then make it clear. This makes your complaint much easier to deal with and also more likely to be resolved to your satisfaction.