Bank authorization?

For the past four months, money has been withdrawn from my bank account in small amounts without my permission. According to the bank, I gave the withdrawer authorization. The problem is, the withdrawer is Google Ireland Adwords, which is in the Google marketing/advertising industry. I called them and they said they have severed all ties between the withdrawer and me and canceled the authorization. There was no action for two months, but now it's started again. I don't know what I can do. The bank can only temporarily block the withdrawer, which I have tried. Can someone suggest a solution, please.