Then why did Paul refer to him as a Doctor in his letter to the Colossians?
That would be like saying “Mary Magdaline, the prostitute”.
Doesn’t make sense to keep using a title to a profession that you consider sinful once you are saved.
But maybe logic is a sin as well.
If it leads you away from the Lord's commandments, most assuredly so.
Luke wrote the Acts, wherein he described the acts. Healing was definately one of those, but not the pagan variety. James describes in detail the process of healing used by the church, in his chapter five.