He was informed by Conte he was no longer part of his plans at Stamford Bridge via a text message earlier this summer.
And now Costa has lashed a new thinly-veiled jibe at the Chelsea boss for his handling of the situation.
He told MC News: "Conte's text? It was a moment of madness. It can happen, but I thought it was disrespectful.
"I always asked to speak face to face with the Coach and the board. I never sent [them] text messages, so it shows what kind of person he is.
"If something makes me sad about this situation, it's [the fans'] affection as they'd always supported me, even during the delicate moments.
"If I'd been in the team for three years, it was for them and the dressing room, which was very much united. It was a great experience."