Recieving Code for Google my business
If it has been at least two weeks since you requested the code AND you have not modified your listing in any way during that time, you should contact support and request their assistance.
Google has changed (actually hidden) their support options.
You can dig to get in touch with Google My Business Support. You need to:
1- log into your Google my business dashboard http://www.google.com/mybusiness
2- select support from upper left hamburger menu
3- a help screen will appear to the right
4- It used to be just a scroll down to contact us under Contact Us
5- Scroll down and select Need More Help
6- Select the specific problem - in your case Verification
7- Select I requested a postcard more than 14 days ago
8- Scroll to the bottom of the page and choose most appropriate contact method for you (some are not always available)
Alternatively you can try contacting them: