A few questions on Arena?

the arena selects your foes based on rank. The highest foe you can attack will always be displayed in the far right panel. you may have to refresh the screen quite a few times to see the absolute highest you can attack.

At lower ranks on the leaderboard you can attack people a lot higher than you on the leaderboard. Once you get into higher ranks, that window of people you can choose to attack shrinks. For example, at rank 12 and below you can only attack people four ranks above you. 13 to I'm not sure what number can attack people five ranks above, and so on.

The other teams you are facing are people that share your leaderboard. if you are seeing teams higher levels and stars and gear than you, then there are a number of reasons for that; from spending resources better, to dropping large amounts of cash.

If you are climbing 50 at a time and getting knocked back before you can even attack again, players may be targeting your team due to a perceived weakness. The only way to really combat this is to focus on your arena team and make them better. There are many, many guides and threads out there to help you do so....