Denial of the flat deal

Hi, I had entered one flat deal and gave token money on written commitment of vacant flat after 2 months of the deal. Its now been 8 months and the flat is still not vacated by the Tenant staying in it. Twist here is the flat was given on lease and the deal was done in between the lease period with a verbal confirmation by the tenant to vacate the house. Tenant still says he is ready to vacate the house but doesn't gives a final date in writing for vacating . All this time the seller didn't give any written notice/ letter tot he tenant to vacate the house. it was always only verbal terms even though we had been requesting him time and again to give it in writing. In month of Oct, tenant committed February month to vacate the flat in from of other residents of the same building and the seller and us. But again he didn't honor his words. In this whole tenure the flat rate have gone up by 20 % in last two months. Now the seller started putting pressure on us to get the flat registered in our name and give full payment and then deal with the tenant ourselves to get the flat vacated to which we refused. Recently we saw the seller posting ad for flat on sale on one of the property site. As a precaution we issued a notice in name of seller asking to get the flat vacated soon and get the registry done ASAP. Seller got offended by this and is now refusing to carry on the deal with us. Point to be noted here is 1) The lease agreement between the seller and the tenant is not registered. Its only made on a stamp paper but was never registered. 2) Our agreement between us and the seller was also done on mutual trust on a simple paper with signatures of both the parties. Though we have many whatsapp msgs and call recordings confirming the deal and our request to them to abide by what was agreed. I am feeling very disturbed with all this behavior by the seller and the leniency he showed towards the tenant. Most importantly post the notice we met once to finalize but his son talked very rudely with me and put all the blame of the delay on me saying I don't have patience. I mean even after waiting for 8 months instead of 2 months he comes into picture all of a sudden and says this rudely.. That guy needs to learn to talk respectfully to a woman. NOW WHAT SOULD I DO ? please guide.