Looks like this is one of those car insurance policies that you bought so as not to have the extra car hire insurance the rental company ask's you to buy, is that correct?
Having been renting cars in Spain for years now I always buy the extra rental insurance, once I thought give it a go via what seems like you have done, so I did, got to the rental desk, told them what I had done and as suspected they didn't much like the idea, as this policy only cost me about £40.00 I wasn't to bothered so took out the extra rental insurance.
Do You Spain I use them every time, correct me if I am wrong the insurance policy you took out was not with them, it comes through a 3rd party company if you wish to call it that, Do You Spain only advertise the option to buy it......Anyway
Came back to the UK and mentioned to the insurance company that what they sold me wasn't fit for purpose, they refunded every penny back to me, no fuss or argument.
Just paid 168.18€ about £131.42 (1.2797 exchange rate) rental car extra insurance for 14 days rental, never had any problems when taking the car back, even when someone bashed in the rear bumper on one rental, stole the roof arial on another.
Might seem excessive costs to many but piece of mind has no price or value, many on here will now say they have never had any issues with buying a UK based insurance policy, me I prefer not to find out.