How do I beat the last mission of the Sforza campaign (A new duke of Milan)?

Playing on hard. I mastered the Dracula campaign, even the last mission of it on hard. It was challenging but doable. But here, you start with no army, no technology and no resources. I already tried to build castles, wall in and use monks, but its unbeatable. Around minute 15 they will send cannons paired with even more knights, its a never ending mass.

In videos I found on Youtube they won't send that mass amount of rams and no cannons. So, how do I beat this mission? Do I need to kill the trade outpost beneath my base?

It appears that they changed the AI further or it is just luck. I get steamrolled whatever I do. When I try to hide it out there is just a greater mass of enemies attacking at once.