How do you actually make a complaint?

The page they send you to, just makes you go round in circles if you want to complain online. I just need to make a complaint, how difficult can it be?….turns out EXTREMELY DIFFICULT 

Gave plenty of notice to end contract, requested PAC code a week early, so now i have to pay out of plan charges, not going to bother to dispute it as that will be like pulling teeth, however, they told me that there wouldn’t be any fees due as i had given enough notice, now though there is an outstanding balance i wasn’t aware of as i had removed the App from my phone...i couldn’t wait to get away if i’m honest as the service is less than poor. 

I left my DD in place, incase there were fees (crafty folks that they are), but nothing has been taken, so thought all was good to go, until i checked my credit score recently and there are two outstanding amounts for ID (as i had 2 phones at the time with them). no contact has been made by ID for Payment and trying to make payment for both phones at the same time is nigh on impossible. I have contacted the ombudsman, but they cant help until i’ve registered it with ID. In a world full of technology, I have since resigned my self to the fact that i’m going to have to write a letter to complain. Which in itself is no biggy, but really???