Battery and its related system problem

Respected sir/mam. I shashank verma s/o R.P.verma has purchased the nokia lumia 520 (black) on 2nd,feb,2014.and till 7th,august,2014 i have visited nokia service centre which is near nilgiri,Indira Nagar,Lucknow.with the same problem of my phone that its charging speed is too slow through my charger which is of more than 10 hours and by chance if i use my phone while charging only for small duration then it just switch off(deep discharge) and again to restart, i have to connect it through my laptop as during that time charging through my authorised charger is ineffective. Yesterday i had also submitted my phone to that service centre and today i got my phone back with that same problem still exist.now i lose all my hope of my that problem to be solved by that service centre,they the workers r also not cooperative . I would request you to please focus your attention towards my problem,and please solve it as soon as possible,i will be highly thankful to you. Yours faithfully Shashank verma Phone no.8604975403 Email [email protected] Add. 5,Rahul vihar,opposite manas vihar,Indira Nagar,Lucknow Post cimap 226015