Also the aircraft I fly is not designed to carry several extra tonnes of fuel, for contigency.
Then plan a tech stop for refueling, or...chuck off some payload and uplift more fuel.
I had this very scenario two weeks ago, transAtlantic and chucked off three tons of excess baggage, as more fuel was needed, due strong headwinds
IF you're a professional (as you claim) use your head and find a solution.
I suspect the Spanish ATC folks could care less about your problem...as they have their own set of difficulties.
I also suspect they will not change their modus operandi anytime soon.