Britt Assombalonga grabbed his second from the spot after Anthony Kay pulled down Conor Washington but Robinson was furious with referee Hill for giving the decision.
"I think the referee's decisions have cost us," he said.
"We missed one or two half-chances and they hit us on the counter attack. Their first goal could have been defended better and then the penalty.
"I've seen it frame by frame and it's definitely not a penalty. Or if that is, then the assault on Giorgio ;Rasulo by Ben Nugent; in their box where nothing is given is just embarrassing.
"And DeleAlli was caught as well. He takes a touch and their defender has caught his trailing foot. I was surprised to see Dele booked for simulation because what do you expect him to do? Get smashed? He's tried to ride the challenge and lost his balance. The kid was magnificent.
"Listen, we've been beaten and we have to accept that but there will be a lot of people leaving here who are very very disappointed with the outcome."