"Part of the signing of the contract," the Dutchman told Germany's Auto Motor und Sport, "was that in 2015 I will drive for Toro Rosso."
Team incumbent and Frenchman Vergne, however, said he didn't know about losing his Toro Rosso seat until six days later.
"I knew about it just before you did" on August 18, Vergne said.
Asked by France's RMC if he appreciated Red Bull's handling of the news, he answered: "I think there is no right or wrong way. And I'm strong enough to overcome this kind of stuff so there is no problem.
"It's pointless to be angry -- or if I do have some anger, I will put it behind the wheel and make a show!
"I am looking at opportunities. Today I am in F1 and my place is in F1."
However, former driver and German television commentator Marc Surer doesn't agree.
"He (Vergne) had his chance. He was against Daniel Ricciardo and didn't prevail, now he is struggling with the rookie Daniil Kvyat.
"This is obviously the worst thing that can happen to you as a driver -- you're in your third formula one season against a driver who last year was in GP3 and you're not really beating him," said Surer.
"Only the best are in formula one and Vergne is not among them.
"He is a good driver and as a Frenchman I could see him on the podium at Le Mans. But I think F1 is over for him."