Are you using any activated carbon in your filter? If you are, it's stripping any medication you add to the water out essentially right as you add it. It's important to remove all activated carbon from your filter when medicating.
I agree, temperature increases and salt work wonders for curing ich. However, if you're medicating, be careful with the salt as many medications include some salt in them as well. You wouldn't want to overdo it, especially as bettas are sensitive to salt.
Also, once your fish get healthy again, that tiger barb is very likely going to destroy your betta's fins. Increasing the school size of the barbs helps reduce their nippiness, but a suitable school of them would be too much for a 10g tank. Tiger barbs need lots of swimming space.