This is a fair question, so let us explain the two things that are happening.
Your premium reflects your pet's age, breed, claims history, and rising vet costs. That is why it can rise at renewal.
Your coverage limit for a previously claimed condition stays at the limit of the plan you were on when you claimed it, even if you upgrade. New or unrelated conditions get the higher limit of your upgraded plan.
So you can pay a higher premium and still see a past condition capped at the old limit. It is not double counting. The premium reflects overall risk and cost, while the condition-specific limit protects the pricing fairness of the upgrade. If you want, we can look at your specific case and show you the limits side by side.