If you failed to pay the full premium, your insurer may legally drop you from coverage. It does not matter why did not pay the extra or full premium, so long as it was not the insurer's fault that you did not pay--and nothing you have written indicates it was the insurer's fault, since they apprently sent notice to the address they evidently had on file. Therefore, they could discontinue coverage.They are not required to reinstate you when you are dropped for a reason not the insurer's fault. You most likely need to find a new insurer.