This is not an issue of Syed or non Syed and amr bil maroof and Nahy Anil munkar is wajib on every individual with the conditions.
We got some work done by a Sayyed brother. He charged us a lot more than he had made the deal. Also he lied outright. Now what I want to ask is, that, if he is lying to us and taking money unlawfully should we just give him thinking of Let Go. Is it possible that we will be asked in akherat that that why did we not do nahi Anil munkar with him and why did we let him consume rizk e Haram
Did you have the deal in writing?
If so you should consult a lawyer and send him a notice if he doesn’t cooperate.