Heavy Cav is tricky. I had the Same thing happen when I was playing against a Heavy Cav Roman Army. Historically, Heavy Cav and Cav in general was tough.
Here is what I did 3 weeks ago in our match. He came with the same Cav Army against my Gauls, so I went archer heavy. I had 10 standard archers with +1 for Shooting II and 5 units also had long range = 35pts. I spread the units out, close but did not group them. When he charged, he could only charge a stand, so he was always getting attacked before he hit and did not hit my combined units. I'd roll on an average(range) -4-6 D6 and try and hit on 5+.
He quickly learned to stop charging me :)
You'll sacrifice some units, but you can also trap any cav army this way. A downside is they are tough to move because you just don't have enough movement points for all of them.
Let me know what you think,
RebelMike