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Sorry to hear about your problem.
Water hammer is typically heard exactly when you shut off the water only. If you hear it when you turn the water on, then you most likely have air in the pipes; you may have both.
The water hammer arrester needs to be installed as close to the noise source as possible. Also, make sure that you have an arrester installed and not just a pressure restrictor. Pressure restrictors are just piping that are made into a "T" and are filled with air, before being capped. This air can eventually dissolve into the water, whereas an arresters air is separated from the water and is permanent. Here is a picture of an arrester.
There are only two ways I know of to get the air out; push it out by increasing the water velocity, or open the pipe and release the air. To push the air out you need to temporarily increase the water velocity to the point the water "sweeps" out the air bubbles. To increase the velocity you need to turn on as many water outlets as possible. That creates a high water demand and the water velocity goes way up. As the water rushes through the pipe the trapped air is swept along with it and out of the pipe. Turn on all the faucets in the house and then flush all the toilets. Again, give it a few minutes to push that air out. If you know where the water supply comes into your house turn off the faucets starting with the one closest to the water supply entry point, then close them one at a time moving away from the entry point. As you come to a toilet when you are moving through the house turning off faucets, flush it again, then wait two minutes before closing the next faucet. Don't forget the faucets on the outside of the house. If this does not help, try the next option.
If the air can't be pushed out, you will need to find where the air is trapped in the pipe and "open the pipe" to release it. Air rises above water, so the air is likely trapped in a high spot in the piping. If you can identify a likely high point turn off the main water shut-off valve and open a faucet or valve to release the water pressure. Then cut the pipe at the high point and install a tee on it with a small valve on the tee outlet. A compression type tee may be easier to install. A 1/2" valve, or even a smaller one if you can find one, will work fine for the valve. Do not use a gate valve, since they tend to leak easily. Ball valves work good. See the drawing below. The valve needs to be on a short nipple, a few inches above the pipe as shown. Close the faucet and turn the water back on. The air will rise to the highest point which is the short upright nipple under the valve. You can then open the valve just a little bit to let the air escape. Some water is going to come out too, so be prepared for it to squirt! After releasing the air put a plug in the outlet of the valve for safety.
Verify that all pipework is secured and supported at regular intervals using appropriately sized clips, as well as securing close to the source. This is very important since loose piping can fail at joints from moving water pressures, not to mention make plenty of noise. Click here for more information
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Best of Luck, Brian
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