So trump was lying when he denied saying "he knew what he was signing up for" and when he said he had "proof" that this congresswoman was lying?
First, you are assuming that Trump was referring to those specific words "he knew was he was signing up for" when he said that wasn't true, as opposed to "but I guess it hurts anyway" or the characterization of the entire conversation. The latter would be the reasonable thing to conclude, unless you are a butthurt liberal looking for a lie.
Second, you are assuming that the only "proof" would be an audio recording, as opposed to numerous people being in the room with Trump when he made the call, which is true.
You're bending over backwards to find a lie, any lie, to excuse this disgusting political stunt. You should really let this go.