Right, I loaded up your save today and indeed, the messenger was bugged, but there was also another bug that prevented you from proceeding. Before Simmons can give you the next mission, you need to know about Cornell and the Acid Hunters. You can learn about them from Buzzer, who you saved, and Hugo, who you also saved and talked to near Foundry. We found a bug in Hugo's dialogue where in certain cases him telling you about Cornell doesn't register properly and fixed it for the next update. Now, you didn't talk to Buzzer about Cornell, from what I saw, so you can do that and then go straight to Simmons and he should give you the next mission (talking to messengers in Core City is not crucial, their purpose is just to inform the player that the oligarch they're working for wants to speak to them).
Short version: Talk to Buzzer about Cornell, see Simmons, play next mission. Bugs fixed for the next version, sorry for the inconvenience.
P.S. Also, you are low on cash. Those stacks of charons and SGS credits are just... not good enough.
