NOT GETTING ANY ASSISTANCE AFTER PAYING THE CAR IN CASH

We bought a car at We Buy Cars Midstream about three weeks ago . We were told that the car ONLY had a SMALL oil leak and that the service History was up to date . The service book was stamped and everything seemed in order , BUT my Mechanic brought something to my attention . I then started to investigate the matter and asked the Dealership for Job Cards as it seemed that the service book was just stamped without any service being done . They could only provide me with 2 jobs cards from 2019 . APPARENTLY they lost the other job cards . I don’t think this is true , and I believe that the car was never really serviced in the FIRST PLACE . If this happens to be the truth , it’s ***** . I do not believe that a job card can just disappear . How can they have the old ones but not the recent ones ? When we got a quote from our Mechanic , he ran a diagnostic and we found out that IT WAS NOT just a SMALL oil leak but the car has MAJOR issues and the engine needs to be redone . This will cost me an extra 30 k . Another concern is that we paid for the car to be registered and I received an email that the car can’t be registered to my name . ( AFTER WE PAID more then 1 k ) .