Samsung Mobiles — internet issue

My name is manish i am from ulhasnagar (maharashtra) having samsung galaxy S duos 7562 this complaint is regarding the internet issue which i m facing since day1... The issue is when i use both sim cards(dual sim mode) the internet connection gets disconnected frequently...i visited the samsung service centre four times for same issue but they just updated the software everytime and handed it to me but the issue is not resolved yet... well there is issue with whatsappp aswell when i receive a message with hindi text font it works very slow... i have approached the customer care for the same but they are not entertaining me now as warranty is lapsed ... however i have approached them for the same since my warranty period and now they are telling me to pay for the issue... please assist me what do i need to do now... Awaiting for your valuable feedback Regards, Manish Sidhwani [protected]@gmail.com [protected] [protected]