Gas cylinder exchange with a non standard cylinder

Avoid this company by all means. They swapped my brand new 13.5kg gas cylinder with a very old non standard one, of which the connection fitting was non-standard which do not fit on the standard connectors. I only found this out at home when I tried to use the cylinder, and when I took it back they claim that it is not their cylinder which in principle apply that I am lying. The cylinder information does not appear on the receipt slip, which left me stranded with no prove. What probably happened is they swapped this cylinder from somebody else wrongfully, and dumped it on me. They did not try to listen to my compliant and were very unprofessional. The owner was supposed to get back to me, which did not happen.