Call your doctor for an appointment. You will want to see if you can get a prescription for a different pain medication. Immediately stopping the drug can cause withdrawal symptoms, so you'll need to follow your doctor's instructions on tapering down on it.
Even though the drug was banned in the U.K. six years ago, the drug was only recently banned here in the U.S.
According to Public Citizen, the side effects (heart problems) will go away once the drug's use is ended.