The actor told Digital Spy that he had started "to lose a bit of faith in the powers-that-be" following the show's cancellation in April.
"I was so surprised - we were all expecting it [to get picked up]," he said. "The writer [Adrian Poynton] had been commissioned to write more scripts for the third series - we had it all story-lined and it was going to be a great series."
Mellor claimed that he still hears from White Van Man fans who are shocked by the show's axing.
"The response on Twitter and people meeting me in the street... they can't believe it, because they got behind it," he explained.
"It was repeated on BBC One and got a great audience. They say it was the highest-rated new comedy for BBC Three ever - bigger than Gavin & Stacey and all that, yet Gavin & Stacey got moved to BBC One and we get axed.
"You don't know why things happen, but they do. We did our job and the audience did their's by watching it. When you tick all the boxes, you expect to be rewarded and instead we were cancelled. It's disappointing and you start to lose a bit of faith in the powers-that-be - if we tick all the boxes and you still axe us, what are we supposed to do?"
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Mellor went on to blame the comedy's cancellation on a regime change at BBC Three, with Zai Bennett replacing Danny Cohen as controller of the channel in late 2010.
"Sometimes when you've got a new commissioner coming in, they want to bring their own stuff to the channel," he suggested. "Our show was commissioned by Danny Cohen, who went to BBC One... so you can get caught in the middle of these little tug-of-wars of who owns what show and who gets the credit."
The second series of Will Mellor's BBC One comedy In with the Flynns begins on Friday, August 17 at 9.30pm on BBC One.
Watch a clip from series two of White Van Man below: