Remove Unlimited Data

A few months ago, I purchased unlimited data for my home internet, because I went over the limit. In June and July, I do not expect to go over the limit. I want to pay for unlimited data for May, but I do not want to pay for June and July. I will probably add it back in August. Anyway, I tried calling to cancel, and the representative really confused me about when to actually cancel the service. I read the FAQ ("The Unlimited Data Option will be removed from your account on the first day of the month after the request is made. You'll be charged for the Unlimited Data Option through the end of the month in which you opted out. You won't be billed separately for any overage charges during that month."), and I thought the representative would know what to do, but she just made it confusing. Of course, I want to do it correctly and not incur any overage charges for May or pay the extra $30 for June or July. Please help. Thank you.