As for the magnesium malate I like Source Naturals and NOW Foods, which both have pure magnesium malate without any added magnesium oxide that some manufacturers sneak in. And I generally recommend 300mg two to three times daily.
If you are taking doses that high and you are not getting results the possibilities include that your condition is not caused from calcium, your calcium levels are severely high such as from hyperparathyroidism, or you are not absorbing the magnesium.
If you were taking a drug previously and it was working then this can tell us what is causing your high blood pressure. This could be calcium, ACE, sodium, epinephrine, etc.