Sandu union deducting after 3 years of cancelation

I cancelled my Sandu membership in 2012 but I still get billed to date.<br> <br> I faxed they a letter requesting to cancel my membership, they promised me it will take 3 months but still it has not. They even increased premiums 2 times without my consent. I want Sandu to refund me all the premiums I have paid since I cancelled.