Item ****** from my car during service

I took my car for service at Hyundai the glen, l mistakenly left a small bag in the car with coins and earpods, under the seat there was also an umbrella and a water Bottle, surprisingly the bottle aka umbrella was there but the bag was moved and tossed in the boot with no items in it. I also had a knife that stays on my drive door which l also found missing and all the manager could say to me was "l spoke to my guys and they say they didn't find anything, that is why we encourage customers to always take their valuable items" so if you forget your items be rest assured they will go missing. Very disappointed at how this matter was handled. I will change from using Hyundai