What are you feedin them? the creep ration, if it's got alot of roughage in it, that could be why they aren't grazing or eating hay. We had that problem when we started feeding our daughters show heifers last year.(had gotten up to almost 20 lbs of feed per head per day.3% of body weight) The bagged feed you buy, beef grower whatever has alot of roughage in it and so therefore they dont need the hay. Hay is cheaper tho than payin an arm and a leg for roughage added to a bagged feed. See if you can find a feed that doesn't have the roughage added. You won't feed as much, but they will then go to grazing and eating the hay. I also recommend a loose mineral. We use the MG Brand 12-12.
Right now we are currently feeding her heifers for this years fair, 7 lbs each of the feed, and free choice hay. They are spring (jan feb) calves and averaged 750 lbs in November at tag in. We started feedin them the middle of October. Last year we averaged 3.8 lbs of gain per day.