Wrong classification sfkl

Hello, I changed the insurance in November 2018. I am now with an Internet insurer. With the sfkl a mistake happened, I was in 16/21, which was communicated to the new insurer and confirmed, one month later the new insurer set the premium clearly high and informed that I am now not in 15/21 but in 1/21. Several calls to the hotline were to settle between ignorance and impertinence, first call information I should the old insurance If nothing has happened, second call information my insurance certificate is not relevant, the (wrong?) information from the preinsurer is relevant, one wants to ask again… Third call, I did not object to the increase and thus had bad luck….That’s not true, of course, I objected to the increase and made the payment subject to reservation, and received a corresponding confirmation by e-mail a month ago. I complain in writing, with deadline until today, no response…. I have the insurer’s suspicion that the matter will be settled. I have two options. Let the too much paid part book back or contact the legal protection insurance and turn on a lawyer. Of course, option 1 prefers to make 2 a lot of effort. My question, do I endanger the insurance coverage by option 1? I’m sure that the insurance should pay me. But if you don’t want the car to be shut down, then you’re a lawyer…. If you know the big union in the public service, maybe you can think about which insurer it is, I can only strongly advise against it. Thank you Alex