my budget isn't low but they say u spend 2-3x of offer which i did !My 2 cents: your budget is too low, expecially for your geo.
My advice is to invest your money in tier 2/3 countries (I got some decent results in LATAM) and let the campaigns run until your budget is gone. Then you can start searching for patterns in your conversions (browser, OS, traffic placement, time, day of the week... ther is a plenty of possible metrics to analize).
Another optimization you will need to do is blocking bot traffic that eats all your budget with fake clicks. There is a good tutorial here:
BOT traffic - How to detect fake hits and what to do about it! | Online Advertising Tips From Matuloo.Com
Good luck!