I am a type 2 diabetic. my numbers have gotten over 200 a handful of times in the past 10 yrs. the last few days it has gotten to 600. and is not going below 300. what could be the cause?

It is not feasible to provide a meaningful answer without knowing more about your diet, weight, and medications. It is imperative that you see a doctor for better control of your blood sugar. It is important to prevent complications from diabetes. For info: https://www.cdc.gov/diabetes/managing/manage-blood-sugar.html

From progression of diabetes to acute conditions among which infections are notorious, a variety of conditions may account for uncontrolled diabetes. Taking action now might save you a trip to the hospital.