The zombie mobs are too powerful, what can I do?

You'll need to grind if you are having problems with the zombie mobs on any level. See our Grinding Guide: https://www.appgamer.com/survivorio/grinding-guide

It may just be a matter as well of just waiting some days and collecting your rewards, in time, and some grinding, you'll pass the levels, make sure that you keep upgrading your equipment and evolving your player.

Use your gems in the shop to open EDF chests to get better equipment - there is no need to hoard all your gems - especially if you are having trouble getting further in the game.

Use the Guardian and evo it to defender. Then get force field and evolve it to the domain. The defender will push back mobs and the force field should evaporate those that get in. Just don't move too much. Get the fuel tank as well (molotov evo), it does good dmg and covers all four sides.

Use the defender or force barrier the force barrier pushes mobs back