Tower(network) and sim is not showing in Samsung on7
What will I do

Samsung S7? They have bricked all of those phones because of the danger of the batteries exploding.

The S7 was from I recall was indeed bricked world wide.

Advice: Get your full refund (everyone I know got a full refund) and then wait for the resurrection model S7.

The word is they will refurb and re-fit these with a smaller battery.

The main problem, from the engineering perspective regarding the S7 battery problem, was that they wanted a really long runtime between charges on the battery, so they designed it to barely fit in the case (made as big as possible), and as it heated up and expanded, it would short circuit, causing the fires and explosions we have seen. The smaller battery will likely not have that problem, assuming that they allow adequate expansion room inside the case.

All that aside, I love my S5. Removable/replaceable battery, plenty of room for heat expansion, a back cover that can easily pop off if this problem were to occur.