Dx osteoporosis & vit d insufficiency, take vit d3 & ca supplements (500mg citrate), can ca supplements be the cause to raised serum calcium?

Yes: Calcium supplements can potentially raise the serum calcium level, but in an otherwise healthy person they would typically not do so. The bigger question is why a 26 year old person would have osteoporosis, and it usually would take more than a vitamin d deficiency; if you haven't had one a thorough work up by an endocrinologist would be indicated.