What is your travel date and what was the schedule change? Posting a few more details may allow other posters to offer better alternatives that you can call back and propose to DL.

DL can force open award space on its own flights but can’t force open award space on partner flights and only DL partners fly to BOM. DL doesn’t fly there with their own metal. If they’re having issues with the VS space, ask the agent to coordinate with the partner or joint venture desk. They may be able to find an option that avoid a super long layover.

Other options may include rebooking out of DEL or BLR if a DEL-LHR or connection via AMS or CDG or out of BLR to AMS or CDG shows any award space. I’m not saying you should do this as you may prefer not to do this and you would have to get to DEL or BLR at your own expense but just trying to propose a possible alternative.