Thanks for the response here. Sorry to hear that your expectations weren't met. From my perspective, the strategy for responsive design on a given website is the responsibility of the theme, not the responsibility of any number of given plugins implemented on that website.
As such, I don't ever actually see Gold Cart making any opinionated decisions regarding responsive web design. Again, very sorry that your expectations were not in alignment with the reality of the plugin. I did check to confirm that Gold Cart does not state anything about being responsive, and it does not, as it should not.
Again, sorry to hear that your expectations weren't met - but my best suggestion at this point would be to work with your theme developer to extend your responsive stylings to Gold Cart and any other plugins that need to be made responsive.