I wouldn't have even opened the door for them.. This kind of thing happens all the time.
They would have just kicked it in then. If they have a warrant they get in one way or another.
Look I'm originally from Washington DC and this shit happens all the time except they roll into your house in SWAT gear with masks over their faces and M22's pointed at your head, no bullshit. Happened to a buddy of mine. Then they toss your whole house, take what they want, film the rest, fill out an inventory sheet, and give you just enough freedom to fuck with your head so that you give them what they want without a lot of hassle...which is a bigger fish than you. All they want is their picture on the front of COPS Quarterly with a bunch of plants and some poor fucker in a headlock. So they need you to get them to the bust of their dreams.
They probably got a few stems and seeds out of your trash after you put it out to the curb or in the dumpster. This is the easiest way for them to get a guaranteed 'no-knock' warrant. This is called a 'dirty trash pull'. That's why I NEVER throw ANYTHING in my trash, I flush it down the toilet instead. Anything that can't go down the tubes gets triple-bagged and dropped off in a dumpster behind a strip mall a couple of miles from my crib.
I don't know how they do it down here (back home they took almost all of my boy's shit and spent hours searching for the nitty-gritty), but unless you leverage the fact that they don't have physical evidence via a lawyer your ass is going to be sitting in jail bro. Don't just blow this off man, start working on your defense. GL