Dealer refuses to withdraw from the contract because “no delivery date has been set.” Is that possible?

Dear community, when I bought my Ceed SW Vision automatic, I was given a delivery time of 3-8 months by the dealer under witness. These 8 months are now around. So I went and announced that I would no longer want to wait and cancel the purchase contract. The dealer then took the contract and said, “We did not hold on to the delivery date, so there can be no delay.” I told him that he would have spoken to him again and again of up to 8 months, but he didn’t mind nte “no he would never do that”. Is there a universal time, which applies even if no deadline has been set. That you have to wait forever can’t be. At some point you have to be able to step back, right? Does someone have advice for me? And yes, if my Ceed is downgraded to 140hp, I’m happy, because then I will probably be able to cancel, but I don’t want to expect that now. Especially since the dealer had me sign a sheet (and I did it dum I would not sign again. Well, thank you for your answers in advance.