If you have a calcified stone then chances are that you also have a number of cholesterol stones that are not detectable on ultra-sound. It is often these other stones which are quite soft that cause gallbladder pain. The pain is commonly caused as the cholesterol stones, which are softish transit through the common bile duct.
Some very hard cholesterol Gallstones do show themselves on ultra sound. It depends on whether they have a surface that reflects sound and a density that it different from the bile that surrounds them
Unfortunately, the only recognised conventional medicine solution to gallbladder problems is to have it removed.
Flushing to expel stones because of gallbladder pain is straight forward. The fear of the pain returning (I've had it) motivates to do something about it. Choose a simple straight forward post like the Hulda Clark .
I have concluded that there is nothing you can take at home as an herb or supplement to dissolve a calcified gallstone. You can start to change your diet so that you can improve the flow of bile; always good if you want to flush. There is plenty written about this subject and loads of confusing opinions. My advice is to read and gain knowledge for yourself; then make up your own mind. The primary factor is the flush itself and all the other things like herbs etc just add a little to the process. Psychologically they can be a strong re-enforcer.
There is no reason based on size why your 23mm shouldn't be expelled except that sometimes they stay put. However, because your will purged the gallbladder of the other cholesterol stones the calcified stone doesn't appear to cause anymore gallbladder pain.
The largest stone reported this year with a picture was over 40mm. (Unfortunately this picture is no longer in the gallery)
PS. If you want to cleanse as part of a change it life style or to cure a chronic illness then you would need to embrace the philosophy of wholesome living.