Walmart family mobile Walmart family mobile bill me for non service month. Store sales rep misled customers Sacramento California

My husband and I purchased two family mobile SIM cards separately in Walmart in May and July this year.We were told by the electronic sales person that since these were contract-free plans, we could just stop using them by not-paying the bills. But I recently received a bill sent from family mobile saying that I owed $163. After that, I went to Walmart Sunday afternoon and talked to the sales representatives. They told me I have to contact family mobile customer service about the bill. I called CS in
front of them and I talked to a guy named Osman. He told me that I had to pay for the bill and plus next month's before I can cancel the service, unless family mobile will keep on charging me, which was totally different story than what I was told when I purchased the SIM cards.

I do not understand why family mobile keeps on charging me for suspended numbers and I should not be responsible for the bill family mobile sent me since the sales representative told me the wrong information.