Massive IT company unable to provide Tech support

I have an email address with Microsoft. The email address is ********** I use the email address for my business. Some of my emails bounce back when I email clients and my clients' emails bounce back when they try to email me. I am losing business and after all my emails to Microsoft they are unable to give me a valid cause of this issue and they will not escalate the issue. They just keep telling the same thing (useless information that I already know) . They also send me emails telling me that they assume that my issue is resolved when it is not.