1) When will you be in the city next?
It's OK but I find "When will you next be in the city?" more natural.
2) The agent always tell me one thing and then things will be completely different in the end.
I find this one rather unnatural.
"The agent always tells me one thing and then does something completely different."
"The agent always tells me things will be one way and then they turn out completely different in the end."
Can I phrase the above sentences in such a ways like this?
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.