I'm sorry to hear about your situation. It sounds like you are dealing with a difficult contractor who has not provided you with a clear and accurate estimate for the renovation work and has not completed the work to your satisfaction.
Even though you do not have an official contract or agreement with the contractor, you do have communication through WhatsApp which can be used as evidence to support your claim. Here are some steps you can take to address the situation:
Review the work completed so far and create a list of any issues or incomplete work. Take photos or videos of the issues as evidence.
Contact the contractor and express your concerns about the final bill and the quality of the work completed. Ask for a detailed breakdown of the costs and an explanation for any increases from the original estimate.
Negotiate a resolution with the contractor. You can discuss options such as a partial refund, fixing the issues with the work, or completing any unfinished work.
If you are unable to come to a resolution with the contractor, you can consider filing a complaint with the local consumer forum or filing a civil suit. The WhatsApp communication can be used as evidence in court.
In the future, it is important to have a written contract or agreement with any contractor before beginning work. This will help to ensure that both parties understand the scope of the work, the costs involved, and the expectations for the completion of the work.