Do you get any signal like 3G, H, H+ or LTE? on your phone? Check your APN settings make sure it is correct. Also make sure you have enough load if your using prepaid.
Pwde mo rin i-soft reset phone mo, hold mo yung power saka home button wait mo hanggang lumabas yung apple logo then let go mo na yung power and home button. Once nag on na try mo ulit i-check kung makaka-connect ka na. Kung ayaw pa rin reset mo yung network setting. Go to Settings --> General --> Reset --> Reset Network Settings.