It seems that you are having big hematoma
at injured part now it gravitated down causing swelling on ankle.
There is nothing wrong in your ankle joint.
Continue applying ice pack 2-3 times a day.
Give complete rest to the part.
go for antibiotic medicine course to prevent infection on the part after consulting your doctor.
If swelling does not subside then puncture of hematoma may require to aspirate blood.
ok and take care.