I think that talking to the Instagram support service might help you. I'm sure it's not that problematic to connect your Instagram account to constant contact. Still, if you are doing this to promote your Instagram account, I can tell you that there are easier and more efficient ways to do that. For instance, companies like https://megafamous.com/free-trial offer you the possibility to increase the number of likes artificially. Which, from my perspective, is a pretty efficient method to make your account more popular.