Road Protect only pays half of claims

I took out a policy with Road Protect about 3 years ago, because damage to tyres, due to a potholes, was covered by the policy. On 11th August I irreparably damaged my rear tyre due to a pothole. I contacted road protect to lodge a claim and after months, was told that they will only pay half of my claim. I am totally dissatisfied with Road Protect. Why say you will cover an issue, then renege on your promise.