You've got two separate agreements here, one with Tesla to buy the car for a set price, and from what you've said that hasn't changed.
The other is with Black Horse to finance the purchase, and it is that one that seems to have changed.
Not sure exactly where you are with regard to the signing of paperwork etc. but in general terms, there is no obligation to use Black Horse for your finance and you could substitute a different lender if you can find one quickly enough...
There should be a cooling-off period for the finance with Black Horse even if you've already signed everything.
Worth a quick look around to see if you can find a better deal, but to be honest, for £20 a month over 4 years I probably wouldn't put any more time into it myself.
The other is with Black Horse to finance the purchase, and it is that one that seems to have changed.
Not sure exactly where you are with regard to the signing of paperwork etc. but in general terms, there is no obligation to use Black Horse for your finance and you could substitute a different lender if you can find one quickly enough...
There should be a cooling-off period for the finance with Black Horse even if you've already signed everything.
Worth a quick look around to see if you can find a better deal, but to be honest, for £20 a month over 4 years I probably wouldn't put any more time into it myself.