Seller demanding exchange three days to completion or 3k price increase

Process has been about 4 months, chain free first time buyer buying empty ex-rental. Last Thursday seller demanded exchange with completion next Friday. It turned out that the seller had not actually provided all the required documents which they finished sending over Monday at 4pm. Seller is still insisting on completion on Friday (just 3 working days now) or they'll increase the price by 3k. I have a mortgage, a partially gifted deposit, and a help to buy ISA to sort out in this time and my solicitor is advising me that this could put me at risk of losing my deposit if there were any unexpected delays.

I don't want to accept a 3k price rise mainly based on principle so I think I need to walk away.