Yes this can be dealt with as you entered into a contract with the supplier and a condition of that contract was that the electric seat would be repaired before purchase, circumstances forced you to obtain the car before it was done this does not excuse the supplier from the obligation that was freely entered into.
Your basic rights are contained in the Sale of goods act 1979 as amended. Part of this act is that goods must correspond to their description and in the 1994 act the term merchantable quality was changed to satisfactory quality which is far more straightforward. If you are getting the run around write and demand the repair is carried out and quote the above act giving a reasonable date by which it must be completed or you will take action, keep a copy and if you wish send it by recorded delivery.