A short, useful read for the Malachain community.
A good complaint is short, factual and specific about the remedy. State what you bought or agreed, what went wrong and when, what you have already done, and exactly what you want: a repair, a refund, a replacement or an apology. Attach copies of receipts and messages, keep the originals, and send it in writing so there is a record.
Give the company a reasonable deadline, usually fourteen days, and say what you will do next if it passes: an ombudsman, a regulator or a small-claims court. Stay polite throughout; the person reading your letter did not cause the problem and is far more likely to help a calm customer. Most disputes are settled at this stage because the next step costs the company more than the refund.
It also helps to talk the subject through with friends or colleagues who have tried something similar. Their experience points out the details that guides leave out: how long things really take, which costs were unexpected, and which shortcuts turned out to be a mistake.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.