cellphone claim declined

Upon losing my phone, I logged a claim with MTN phone insurance, submitted all the documents needed and after paying every month without fail, without skipping a payment I was told my claim was declined due to the phone having a different network simcard in the phone the time it got lost. The first agent I was speaking to, Zama, said to me, " it was declined due to using a different network sim and not supporting MTN." Second agent Bonolo told me the same thing as Zama, excluding the "supporting MTN" part. They are still generating a letter which I believe will confirm the same thing the two agents are speaking of, however the confusing part is that is it mandatory for one to be using an MTN network on the phone for claims to be approved? It's a personal phone at the end of the day, it's baffling that an individual is restricted to one network because they took out an insurance coverage with it