Device charge

We got an email from a Colin at Nimble Group saying that we are under debt review as to non payment. We have been going back and forth with emails correspondence, asking as to why Autopage did not take the money off my account for the device fee, when they took there last payment before transferring me over to Vodacom. This is a year later and they are asking for this money now only. Is anybody else experiencing this problem. My friend was with Autopage as well and she did not have to pay for a device charge