Orange technically don't have a complaints department, they have an escalation procedure, you call them and ask to speak with a manager, a time frame will be agreed for the manager to call you back, this is in line with what's referred to as the ADR process, this process is regulated by Ofcom. I would advise you to allow the answering Customer service representative try and help you first though and please be polite as isn't the Csr fault. If your contract call 150 or 07973100150 if your PayG call 450 or 07973100450, 25p charge for PAYG.
All terms and conditions of your contract our on there website, www.orange.co.uk/terms