When you went back to your primary care provider after taking the vitamin D, did he do a repeat EKG to make sure it was ok? If so, I would see if he would write a letter on his letter head to the clinic stating his findings and have him put a recommendation in that letter. Are you still taking the Vitamin D? I am not sure if it would help but it is worth a try.
Don't give up. Nothing can be gained by giving up.
Talk to your primary care provider and see if he/she is willing to help