Help please! Radiator BTUs

We have had a plumber in, we originally had a black milano aruba radiator 1780 by 580 (best heating company) (vertical) in black and btu was around 8866 at 65. Anyway this one started leaking and asked the plumber to replace. He turned up with a radiator 1600 by 445 in anthracite grey telling me that it was more powerful than the one we had... 12000btus he says. Apparently size doesn't matter when I pointed out it was significantly smaller. We then discovered a blemish on the coating and that it was leaking. Called him he said he would arrange for a new one. He arranged it and we were going on holiday. Leak didn't seem to bad so decided as it was tight in timing he could do when we got back. Mornings come and the kitchen feels cooler and we start to suspect this isn't the 12000 btu radiator he claimed he had fitted. Asked him for specs initially he replies with got what you wanted. Clearly not. Called him up again and asked him to provide specs. He complains about not trusting him and that our original radiator never ran at 8860 btu. The specs he sends 2 weeks later don't have the height, they have the width but no column headings. This was my reply to him.... I completely get that we won't get the btus suggested in the specs and it all depends on the settings on the heating system etc My point is that I want to compare the 2 radiators side by side by what the companies say they can achieve on paper. For that I need the spec saying at what temp the btu is listed as per the spec and the height of the rad. I have everything else from the pic you sent me. This will resolve all the issues and settle our minds. Am I being unreasonable? Am I being a silly woman because he is certainly making me feel like one! Suspiciously the picture he sent me when we negotiation price looks like a plumbworld duratherm. Please help! I really want to trust him!