(Telecompaper) Customers of Australian MVNO Kogan Mobile have been told to change to another operator after Kogan's wholesaler, ispOne, went into voluntary administration, ABC News reports. Telstra, which provides the service to ispOne to resell, told Kogan customers that they will not be able to top-up their account and that existing credits will expire within thirty days. The company advises the 120,000 Kogan Mobile users to transfer to another mobile operator immediately and is migrating the customers to a temporary plan in the meantime. IspOne provides wholesale prepaid connections to around 250,000 mobile customers in total, including Kogan Mobile and Aldi's Medion. The latter signed an interim agreement with Telstra to continue services. Rival Optus has launched a special promotion for Kogan Mobile customers. ispOne's administrators, Ferrier Hodgson, has said that the company's debts appear to be around AUD 30 million and said there were twenty to fifty creditors. For fixed telephony and fixed internet services, an agreement is in place as well as for postpaid mobile access, according to administrator Stewart McCallum.