Change SF class to wrong?

Good day, 5 days ago my SF class was graded back to 1/2, on the grounds that the pre-insurance (AD) did not transmit the SF class. BY FAST OF A WHOLE YEAR. I only drove this transition car for 2 months, before that I was also with the BD. It turned out that this had already not transmitted anything to the AD. From my father I had the SF class 10, but I myself only had 6 years behind me apparently. Jetz comes. I wanted this now on m I have transferred (22.05.2013). The AD then told me quite big no problem we do… I did not know that the 10 then becomes an SF6. No one told me, although I had indicated as driving license acquisition in 2007. But they also definitely did NOT do it, although they had received all the documents for the transfer. So I see this as a failure of the pre-insurance, since they did not act immediately what would have said I would not have done it either. It’s definitely too late for me and I don’t realize that I’m paying back or accepting SF1/2. Conclusion after countless annoying phone calls is: the old contract from my father was NEVER touched! Instead, they grade me up as if I had just started driving last year! Is it even justified to come along after a year and change the SF class? I knew nothing about all this and thought it was all right. A well-known lawyer said as soon as the contract is concluded and paid, they are not allowed to do so anymore. and I have already paid one for the summer car and for the winter car already complete. If I go to the supermarket, then I pay e.g. also 1€ for the liter of milk and the owner can then not demand after 5 days 4€ only because he thinks it is right or? MfG