Should I wait for official written statement that my car is a total loss before I purchasea new car?

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I am going through auto collision claim process with my insurance ( first time) and the Claim Adjuster called me to confirm the vehicle is total loss as the damages exceed the value of the car. Its been 2 weeks since they confirmed it over the phone and I was provided a rental car meanwhile they finalize the payment. I also started test driving new cars and I found one for a very good deal with 0 APR.

I left voicemail and emails regarding this but I didnt get back any response from the Adjuster since a week.

And my dilemma is, can I start financing new car or should I wait for the official proof of loss statement from the Adjuster? How risky is it to move ahead with the new car now until official statement?

please advice.