Gyser not working

I'm very disappointed with Leroy Merlin Alberton branch. On the 5th of September 2026 bought a gyser it was installed on the 13th September 2026 my electrician told me that the element is not wrrking on the 14th I went to the shop to complain and I was told to send the picture of the installed gyser and a code on the back of the gyser now they want a COC from the plumber and many many things Looking at the warranty has not even expired. Please assist.