I am just going through this process. The dealer told me there would be no penalty for early settlement. I settled, as agreed with the dealer, after 14 days, however, Toyota Finance have added 56 days interest charges. The difference between the dealers settlement figure and Toyota Finance settlement figure is just over £300.
I have all my communications with the dealer in writing, so have all the info I need to prove mis-selling and have asked for a refund.
Toyota Finance just written to me and threatened to reinstate the agreement and charge me £3600 of interest. I have settled in full, so I don't see how they can unilaterally reinstate the agreement.