If you said anything even remotely like what the client claims you said to him in his feedback, and really behaved in the manner the client says you behaved in, that feedback is the least of your worries.
That would be incredibly unprofessional behaviour and possibly enough to get your account suspended.
Funny how there are always two sides to every story.
By the way, asking for good feedback in exchange of a low price is a violation of the terms of service. That alone could threaten your account.
If I were you I'd very much reconsider drawing Upwork's attention to yourself, your communication with that client and your profile...