Post office? Please help me.who do I talk to about my mail either not bring delivered or going…

Post office? Please help me.who do I talk to about my mail either not bring delivered or going missing. I've bad mail that I know for a fact should've been delivered by now and it hasn't. My SO went to go get a new license and his paper one expires in a couple days. It should've been here by now. Most of his job is driving up and down the road. And I should be receiving several cards by now (cash app) and they never showed or something. I'm getting tired of this. I've been late on deadlines because my mail never showed in time. Idk what to do because I'm supposed to get a financial aid card in the mail and I'm scared it's not gonna show