When you can complain. You must complain to the ombudsman within 12 months of your supplier telling you their decision. If your supplier hasn't given you a decision you might have longer than 12 months, but it's still worth complaining as soon as you can.
How long before I can go to the ombudsman?
You usually need to complain to a business or to us within 6 years of your problem happening. If you haven't done this, we can't usually investigate the complaint unless you made your complaint within 3 years of becoming aware (or when you should reasonably have become aware) that you had cause to complain.