Can I trust the other driver’s insurance company?
Because you are here looking for more information, you already suspect the answer to this question.
The insurance adjuster is probably being rude, abusive or may be ignoring your phone calls. That tells you something about his priorities. Consider who makes money if the insurance company gets away with paying you less than your case is worth. Why would the insurance company offer you anything even close to a fair amount if it can get away with paying you less? How will you know if the amount the insurance company offers is fair?