It should be as easy to withdraw as to give consent. If consent is withdrawn your company/organisation can no longer process the data. Once consent has been withdrawn, your company/organisation needs to ensure that the data is deleted unless it can be processed on another legal ground (for example storage requirements or as far as it is a necessity to fulfil the contract).
If the data was being processed for several purposes your company/organisation can’t use the personal data for the part of the processing for which consent has been withdrawn or for any of the purposes, depending on the nature of the withdrawal of consent.
You’re providing an online newsletter. Your client gives their consent to subscribe to the online newsletter that allows you to process all the data on their interests to build a profile of what articles they consult. One year on, they inform you that they no longer wish to receive the online newsletter. You must delete all personal data relating to that person collected in the context of the newsletter subscription from your database, including the profile(s) relating to that person.