Telkom device insurance

I logged a claim for my lost cellphone, which is insured with Telkom simce 2021, I have never claimed nor have I missed a premium. The contract thaf I signed when I took out the insurance stipulated that my excess is 10% of the value of my phone, to my surprise when claimed now I am told that my excess is 15% due to the change in underwriters. I am very disappointed in the service that I am receiving from them. I work in the insurance industry myself and I know that you cannot change my excess without my consent, it makes no sense that my premium increased and further increased my excess. I called to rectify this and I was told that they will investigate however there is no turnaround for the feedback, in the interim I am siting with no phone, whereas I have been paying for insurance for over 3 years.