Why Cant I Lower My PH?

The problem is that your water is so hard, it contains so much buffering, that the peat infused water may have a pH of 7.4 when you add it, it won't be 7.4 for very long. Altering the pH of water is notoriously tricky, the harder the water, the trickier it gets. At your level, very very hard, it's a cross between witchcraft and knitting sand  As Sue says, it's best just to concentrate on the hardness and let the pH find it's own level.

To reduce hardness, you have to use R/O water as you are doing. With the regime you are following, the hardness will settle out at about 12. You will have gone from the top end of very hard to the bottom end of very hard. To go further, you will need to use a larger proportion of R/O water.  I wouldn't get too carried away if I were you, the fish you have aren't ones that demand soft water. You could increase the amount of of R/O water to 15%, ie half of the replacement water. This would, eventually, reduce the hardness in your tank by 50%.

Your KH is not that high - it needs to be the same as your GH to cause real problems with lowering the pH.
As for substrate, what causes the problem is when the substrate is made from calcium carbonate. That could be crushed limestone or crushed coral. Some types of sand are limestone/coral as well. Those dissolve, increasing GH, KH and pH.
If you can fit the peat ball in the filter,that would be more effective. Or even use a small filter just for the peat.

Chemicals are indeed not the best way to alter pH. Most just lower it temporarily, then it bounces back which is not good for fish. Some of them contain phosphate which encourages algae. And adding chemicals adds minerals to the water, the opposite of what soft water fish need.

I would stay with the one peat ball for a while and see what happens over a few weeks. Once you know that, you'll be in a better postition to make a decision about a second one.