POOR BEFORE AND AFTER CUSTOMER SERVICE

In April 2022 I went to Cashbuild to replace a broken window and then when checking the paints a paint person convinced me to buy paint as the war in Ukraine would cause the prices to go up. I was convinced and bought paint. I told him the color of the kitchen units and told him I was looking for a color that looked like the color on the tin. He sold me the paint. In June I left the painter to paint only to come back home and find a navy grey color. Now, I didn't know that that was the color until I checked the color patch at the back of the paint tin after the paint was app**** to the wall. I called the store (Meadowlands branch) trying to explain my dilemma and the misleading by the Cashbuild employee but the manager told me "what if I was not telling the truth?". I was left with egg on my face after such customer service. I usually buy my hardware things from the Meadowlands CashBuild. That cashbuild employee had the opportunity to sell me the right paint and color, all colors were in the store, I trusted him, how was I supposed to know that he didn't know how to sell the right color? What's the point of having people help us when we will be sold the wrong things? I feel hard done by cause I if I was not convinced and assisted I would have no one but myself to blame. I still have a "navy grey" kitchen instead of GREY! Please HELP ME!!