Hi - Sorry, there is no "way around" the licensing rules. If the serial number has already been used, the game has been registered to an account permanently and cannot be transferred. I would suggest you return the game to the place it was purchased, explain that it's unusable and get a refund. SimCity frequently goes on sale; you may want to watch the sales at Origin.com. In fact, as of this writing, I believe it is on sale https://www.origin.com/usa/en-us/store/simcity/simcity/offer-selection
Be aware that SimCity will not run on MacOS Catalina or later since Apple dropped support for 32-bit games. If you have a Mac running Catalina, you can purchase a single user version of Simcity Complete from the App Store.
P.S. I moved your message from the other post as it was in a thread that was from 2015. Please try not to necro threads