Yu — Network fluctuations

Address:

Nawada, Bihar, 805103

My phone is yu yuphoria and network is fluctuating.4g network is full in that are so that is not network problem and i have used my sim in another 4g phone and it worked very fine and i can call for hours by another phone.
I have visited micromax service center with my problem they are not giving any solution and also don't know how to cheek the problem.
Please sir give any solution for fluctuation of 4g network in the phone. And please don't say it's network problem because if there is network problem same sim also should not work in other phone also.
Thankyou