Threatening action from contractor and took money without completing the house as per agreement.

Dear all, I have given a contract to one of the private contractor Vinay s Patil to build my house (1200 sqft), for 18 lacks , needs to complete within the 6 months . But the contractor is not working as per the design , he provided the wrong design with different elevation. After rcc roof slab work, we got know he's doing wrong execution, after checking with another engineer with contractor , Upto that time I have paid 10lacks, due to this issue we had a discussion with the contractor for continuing the work , and we came conclusion with owner will pay each and every material and labor cost from his hand through this contractor only , but not the old agreement, (because already wrong execution done from contractor , so to continue work), and he agreed and also paid by my end. And at end of building construction he asked another 2.5lacks with old agreement. (He claimed he's working for the building and he only completed the building work) and came with gooans and locked the construction work along with his father ,( he's from army retired officer , ) threaten me to pay 2.5 lacks , otherwise they file case against me from army officer like ,,,and I given 2.5 lacks to them ,,but Here work also not done as per agreement, and even some of defects are in the building which are not rectified and even he's not done rrc waterproof, exact plumbing ,,, Is this any way to help on this.