j7 prime network issue

wow what a mobile is this if one sims network goes down another sims internet connection will get off or it wont work properly till other sim works properly and if 1 sim network show full network connection another one sudfenly shows no signal and same vice versa both sims act like same.first there is was no issue with vodafone sim now even i changes sim from slot 1 to slot 2 it acts same like a mental.till the mobile service happened it was working good now after service both the sim act like mental.keeps on fluctuating and sometimes while using some apps it wont and if when while i am dling any transacyion of bank it starts like this due to which so many times i could not complete transaction and money got stuch for few days and afterwards i recieved refund.i even showed to service centre people they said there is no problem and all but same problem is there