Call them and bug them. 800-274-2538 I have been calling them for the past five days bkz I have had no bars for 5 days. They told me yesterday that a tower was being repaired, but that it was now serviceable. Today, with still no bars, no calls getting through and no calls outbound, they tell me the tower broke again. I live in Philadelphia....big city. Why the problems? I told them I will probably switch to Sprint if they can't resolve this. Once resolved, if ever, they told me they will issue some sort of credit. Yeah, why am I paying for no service and no reception?
Hope your problem resolves. If not, switch companies. Find out what your friends are using. They even had me buy a new SIM card. That was supposed to fix it. Not.
First thing to do is to run a check by measuring your phone's signal strength in decibels. I've discussed this elsewhere but signal bars are by no means the best method for telling how strong a signal you are getting. This article tells you more and the site has some outstanding tips on improving your phone's reception. Message me if you have any questions.