Car Service History

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Hi, help needed please.
Purchased a second hand car from a car dealer. Adverts on website, Instagram, information brochure all state car has full service history. Text messages and verbal discussions from and with dealers say the same. Also said car had one owner but transpires it has 3. Handed a pile of jumbled paperwork on purchase. It was not until I managed to read through it and then contacted manufacturer (Audi) about one month later did I find out that the car did not have a FSH. I did not sign anything to say that I confirmed FSH on purchase. Contacted Dealers and they have rejected my concerns. Have sent 3 further letters saying that the car is not as described and asked for cost of service, necessary fixes and devaluation costs of car because of no FSH. Dealers ignoring my letters.
Please can anyone advise me. I intend to take to the Small Claims Court and am planning to send them a 'Letter Before Action'. Advice about how I go about going to the Small Claims Court would be appreciated too.
Thanking you in advance.

[DE DOGS]

Information for the future, when a car goes for service, it is logged on the computer at the main dealers, also that way the odometer/clock cannot be set back, and also all records are recorded.