Hello Franklin.
Your report of your treatment by this dealer is very disturbing and a number of fronts.
Firstly, Your warranty is established in law through the sale of Goods Act. A seller cannot cancel it. It is automatically part and parcel of the contract you establish when you agree to purchase any new retail product and depending on the reasonable life expectancy of the product can last up to 6 years.
In essence the warranty confirms that a product is free from design , materiel or workmanship defects at the point of sale. It also confirms the product will be fit for its intended purpose.
These are your statutory rights, and they must not be confused with the manufactures guarantee.
A manufactures guarantee is a separate contract between you and the manufacturer (not the dealer) again the dealer cannot unilaterally cancel the guarantee. That can only be done by the manufacturer who is the other party in the contract.
I think you need to report the incident to trading Standards.
I also think you should seek professional legal advice about how to present a claim through the SoGA legislation. The CAB may be able to help or you might get quicker results if you see your own solicitor.
A note of caution though. You have not indicated how much you were being asked to pay for this repair, but it may well be that to pursue it through the courts may cost more than the value of the repairs, and there is no guarantee that you will win or be be awarded your costs.