Brake pads don’t fit into the calipers This is my first time replacing the brake pads of hydraulic brakes. 
I removed the old ones and the model was Shimano B01S Resin, so I bought the same ones.
However, when I have replaced them. They don’t fit into the calipers... well they fit but there is no space for the disc between the pads.
I have drained the brakes completely and nothing...
Does anyone has an idea about that?

Thanks in advance. I have attached some pics about the issue.
I got to fix it just pushing back the pistons with a plastic card. Once they are in their position there was space enough like to set the wheel and the disc brake in it.