Abrupt cessation of beta-blockers (such as atenolol) can sometimes result in the symptoms you describe, however it sounds as if a tapering regimen was recommended. If these symptoms are persistant, you should discuss further treatment options with your doctor and perhaps use a long taper duration.
You're not supposed to stop beta blockers like atenolol cold turkey, you're supposed to gradually wean yourself from them over a period of two or more weeks, otherwise, you get the rapid heart rate you have experienced. Your doctor should know this, tell him what you're experiencing and ask him about a schedule for reducing your dosage over time.