Welcome to the forum, your highness! And welcome to AutoCAD!
My first stab at this is to have you check for metric vs. imperial on both drawings (the door block and the building) and on the inserting of the block.
Check the properties of the block for insertion scale and insertion metric/imperial.
That's the easy and first thing to check.
If those don't work, I would ask that you post the dwgs and let some of us take a look.