If the cal-hypo is not raising the calcium levels in your pool there aren't really many reasons why. Here's what I think they are:
1) You could be losing water and constantly adding more, as Chem_Geek pointed out.
2) Your reagents are old and not effective and need to be replaced
3) You are running the test incorrectly
4) You are testing with strips which are VERY difficult to infer exact values from (I find them worthless for CH and TA)
5) You simply aren't using enough Cal-Hypo and calcium isn't effectively increasing.
6) You are wasting your money on the 48% stuff instead of the 62-68%. WalMart pushes that junk instead of the good stuff. It only SEEMS cheaper.