Unable to activate serial number on second device

I have recently purchased a new device, a mac device, and I am trying to activate my serial nnumber to use the program on a second device. My first device was a windows, I don't know if this is what is causing the issue. But either way, It tells me that I have an Invalid code. Customer support has told me that I already have the serial number activated on 2 devices, even though I only recently bought a second device. Also, when looking in my account, it tells me that I have no devices activated. I want some kind of resolution without having to delete and deactivate the one and only device that is working.