Can anyone tell me what the process is for filtering records that DO NOT contain a certain tag?

I.e. I have a tag on each record if they have Facebook and a tag if they have Linkedin. I can filter for records that have either of those tags but I cannot filter for records that exclude those tags. Eg, I can filter and find all the records that have FB, or Linkedin by using Social media (User defined field) contains FB, but if i filter for records using Social media DOES NOT CONTAIN FB my returned list still shows contacts with the FB tag. What am i doing wrong?

Thanks