Leaving aside that these treatments are a complete rip off (you can do it yourself for around £20), a dealer simply cannot charge you for this unless you have specifically requested it. If they have applied the treatment without your consent then that’s their loss and your gain. Anyone who agrees to pay a penny towards it is completely mad IMHO and dealers who try strong arm tactics to make people pay for all or even part of this ‘service’ should be reported to Motability.