Claim for bad trade practice and service.

I am from Pali, Raigad. My bungalow's construction was working with advice of civil engineer. But after comlpetion of slabs, i found cracks developed on the top of rcc slab. I asked engineer who supplied design for slab and visited before concreting to see steel framework. He come to see problem of developed cracks and started blaming me for not using proper material, then he took concrete sample of my rcc slab and carried over individually for testing and whose report he showed M6.21 grade which should be M20. And he put total damage of building on us. I had taken second opinion and carried out structural audit whose reports said, the design provided by ur engineer is completely faulty and caused damage of building. Reports illustrated that no one span of my building is one way design but ur engineer has designed it one way instead of two way design. So i had sent legal notice demanding damage of my building. He legaly replied that i have not given u any design so there is no chance to claim ur damage. Now the points he thinks to be safe... 1. My brother and mine blue print are in one plan which he signed. He accpted that i have given u only blue print which is in one plan but i was not given any steel plan. 2. I have payment entry which i made to him by cheque, but he says that payment was from ur brother's construction work's balance payment. 3. I have mail showing footing plan which is sent by his office before payment, also have whatsapp chat his computer desktop snap showing rcc one way design. 4. Only things that i don't have are a)Agreement betn us, b) no any hard copy of steel design signed by him. I have filed case in state consumer court mumbai. Plz give advice.