ACP, in this case, stands for "Automatic Colt Pistol." Colt invented the round for a gun of theirs.
Other manufacturers really, really don not want their own ammunition associated with Colt, so they refer to the ammo as "Auto" instead. This is true with .380 ACP and .45 ACP. Seems like there's another one that I'm forgetting.
Anyway, it's the right ammo for the gun. Just a different name for marketing reasons.
As far as the gun acting up, new guns often need a break-in. Disassemble it, clean and lube it thoroughly, then start shooting.
Hi-Points are actually decent guns, accurate and reliable. They cut a lot of corners to keep the price down, but that doesn't mean the gun isn't good. Give it a fair chance.
First, buy as many different brands of ammo as you can find. Just one box of each, but shoot some of each through the gun. It may have preferences, semi-autos often do.
Next, just take your time. Don't judge a gun before you've put 500 rounds through it. If it only wants 5 in the magazine for now, do it 5 rounds at a time. As you shoot, the moving parts rub against each other, and polish each other.
Take it apart every 100 rounds, clean and lube it thoroughly, then keep shooting. Do that 5 times.
Also, get your hands on another magazine. The problem you are describing could easily be a mag problem, not a gun problem.
My Hi-Point carbine technically holds 10 rounds, but it's mighty difficult to get that 10th round in, and impossible to seat a full magazine in the gun with the bolt closed. However, aside from that quirk, it's one of my most accurate carbines, and it is 100% reliable. I've put hundreds of rounds thru it in a day with 0 malfunctions.
Have faith! Have patience! You will be rewarded.