My shots bounce. Not all the time as I did manage to kill a t67 today in the Marder 38T. It was already damaged and I finished it off. I aim at the hull and they bounce, so the next battle I aim at the turret and they bounce. Actually "they" is the wrong word as I only get one shot. I don't carry any gold and while I do carry some HE I never think about loading it, as if there is any time in the first place.
Earlier today I was at the Steppes in the AMX 40 guarding the cap while everyone else took off to the flanks. After a while a Lee went rolling across the plains and I shot it. The AMX40 has binocs and there were 2-T67s sitting out of my view range. I was dead before I could reload or even move.
My only tier 3 tank has the 37mm gun. The tier 4s have the long 50mm, the 75mm's, and the stug III B has the 105. The stug is the only one that has not bounced as it uses HE only, although the long 75s have penned a few times.
At time of writing, your profile shows AFVs up to a maximum of Tier IV; if that's correct, you should be having at least some trouble with T67s (assuming their drivers vaguely know what they're doing), as they're at least a tier higher than your vehicle.
If you're facing higher tier (than you) foes, when playing Tier III-IV vehicles, it's a good idea to play more conservatively; hide as much and for as long as you can (whilst taking shots as opportunity presents itself) - how dangerous you are effectively increases as the game progresses (assuming your team-mates are doing damage and assuming you preserve your hps etc).
Also, be aware that the moment you fire, you are generally visible to blind people with buckets over their heads; get back in cover as soon as you can - one of the things that took me ages to learn is that you will often do more damage overall if you hide after taking your first shot than if you stay exposed to get a second (assuming you face more than one foe).