Coverage

I have a pocket router with a data contract yet I have had no coverage since August 19th I went to a branch and the staff member told me that if there are many people on the tower it won't pick up network (don't get how that's my problem) called the coverage department 3 times already and no help, I went to another branch they attempted to assist but also at a loss ,I am now sitting with data that is going to expire tomorrow that I cannot use and this is very pathetic to day the least