Mollen Immunization Clinics Wants to charge me for what i was told was free Scottsdale Arizona 85255, Internet

On October 19th 2011 i was shopping at the Wal-Mart store in Troy Missouri and my wife was goiing to get a flu shot at the same time. I went with her to the nurse and shot table and asked how much the shot cost. the nurse told me it was free. I told her that i didn't have the part B medicare and she said it did not matter that the shot was free.. i got the shot and three days ago i got a letter from Mollen Immunization Clinics that they were having trouble processing my claim. I called them today 3/22/12 and talked to someone named Daniel. He asked me regular questions and i told him that the shot was free. He said unfortunately it wasn't free and i needed to pay for the shot. I explained three times and he said i had to pay for the shot. I told him i would not pay for what was explained to me as being free and he said well we'll just keep sending you a bill.. I think i got ripped off..