What to do if i am offered money to close my claim?

You can always "ask" for more money--that's negotiation. But you can't force them to pay more other than by threatening to sue if you don't get what you want--it is voluntary on the part of another party (or their insurer) to settle, so all you can do is try to convince them that is in their interest to offer you more, such as to avoid litigation. Of course, if you reject their offer and ask for more, they could "call your bluff"--that is, withdraw the rejected offer and let you sue them. Since lawsuits are not certain--you are never guaranteed to win--take time, and cost money, if you were to sue, you could spend money on the suit without getting anything back; or even if you do win, if the difference between what they had offered you initially and what you did win is less than the cost of the lawsuit, you'd come out behind as compared to if you had accepted the offer (Monetarily, that is; that's not even counting the time you'd spend on the suit.)
You write that you were already paid--the money you used to buy the new vehicle. Unless you have significant other losses which had not been covered by that payment (out of pocket medical costs; lost wages; etc.) or you suffered some long lasting or permanent life impairment or disability, it may be in your interest to take the additional money to close the claim without having to sue, since unless you have significant additional losses, costs, or injuries, the cost of suing may equal or exceed the additional amount, over what they are offering, that you would hope to get.