After 5months of complete hepatitis a&b vaccine i went to check my blood its has 265miu/ml but now after 9months i check my blood only 13miu/ml. why?

You're immune: Assuming this was a test for hepatitis B antibody from vaccine (HBsAb test), it is natural for the amount of antibody in the blood to decline over time after successful immunization. Recent research confirms that protection against hepatitis B is complete for years and probably life long, even if no antibody can be detected at all (assuming you had all 3 doses of vaccine).