The H or 4G only shows where the carrier has deployed the gear and towers in your area. There is nothing to fix on your end 99.99% of the time.
Did you head to their support counter on this? I did and for my phone they told me what areas they deployed 4G.
A friend of mine has the A5 and when he turns on cellular data it doesn't show the H or 4G icon on top and Internet is not available and he has megabyte how can I fix this ???