Poor quality product

On 15 November 2019 I purchased a 20 litre Colourlab white from Leroy merlin. On the container it had a 5 year guarantee. I chatted to the paint consultant and he reassured me that as long as it was stored under dry conditions, it would be fine. I opened it for the first time on 1 August 2022 and discovered that it had gone off. I took it the Fourways branch and was told by the manager, Mr Hensley Andrews, of the paint department that there was nothing he can do but that he would chat to Colourlab. It's been 2 weeks he has not responded to any of my calls. Is this the service we should expect from Leroy merlin. It seems like they are not interested in customer service. There was no "use before" date or expiry date, or anything indicating any shelf life of the paint.