A doctor or practice has no obligation to make sure that you have another doctor lined up, and they are allowed to discontinue having you as a patient if you cannot pay, which includes not paying cash if that's how they operate, or if you have insurance and they have dedicated themselves to carrying for those without insurance. The law does not require doctors, therapists, counselors, etc. to see any given or particular patient, and does not guaranty you the right to a seamless transition from one practice to another.