Can not Receive Email on O365

I can send emails but can not receive them from my email accounts. There is no error message.  I can only tell the emails has not be received because I email myself from a Gmail account and no messages comes. Hadnt had any messages for since the beginning of the month.  I have called the contact support phone line twice only to be hung up on and now the chat personnel has directed me to come here for help? Can someone please assist me. Thanks