Ordered food delivery from local restaurant via Postmates. The food came but not with...

Ordered food delivery from local restaurant via Postmates. The food came but not with the special instructions we entered on the app. One of us has extreme glutin sensitivity and asked for gluten-free bread. I needed the hot sauce on the side since I can't eat much of it due to side effects of chemo. The food came with regular buns and my chicken was slathered with hot sauce which I had to wash off with water* could not eat the bun as it was saturated with the sauce. I called the restaurant and the special instructions did not get to them. In the past, when ordered directly through the restaurant's web site, they phoned us about the special instructions and were extremely helpful. We ordered using a friend's smartphone and my credit card. I want to complain directly to postmates but their web site instructions assume that I have a smartphone or some devise by which they can send me 'a code', presumably by text. No can do here, just have a home phone. They do not show a phone number anywhere on their 'Help' page. How can I get through to them? Their app is cr@p. Plus the delivery guy is a fool. I will be billed $*** for food that I would have sent back if it was presented to me in the restaurant. We would have gone to the actual restaurant if my health permitted it. Never, ever would I use their service again.