Interior work left incomplete

I have a rented office space in IndiraNagar Bangalore. We hired an interior developer to get some interior work done in the office. We agreed on a sum of 6 Lakhs for all the work to be completed in 3-4 weeks. This guy took 5 lakhs payment and kept delaying the project for no obvious reasons. Finally, after waiting on him for almost 6 weeks, we asked him to stop and got the remaining work done ourselves by incurring extra cost. Now after all the work got completed, that interior guy came back and gave us a invoice much inflated bills of around 7.2 lakhs plus taxes. And he is harassing us to make the payment. A couple of point to note: All the agreement mentioned above was verbal and we had not signed any agreement. But we have email trails to support all what i mentioned above. e.g. we have emails, where he agreed on doing all the work for 6 lakhs. In all this delay, we already incurred a huge business loss and rental loss of the premise. We need opinion on how to go about legally for our case.