They sell Bad battery in the name of warranties knowing very well that they are problematic

I bought a brand new battery in November 2025, from battery centre Krugersdorp, I was in desperation situation, as I have returned the second hand one back to them several times already and they would boost/recharge every time. Long story short, with the new one giving me problems, I was advised to take my car to an electrician, the car was checked and it had no issues, because of work commitments I decided to buy another battery and return this one, today I made time to do so, and I am told that I can not be refunded, I no longer want to have products from the battery centre, what must I do with the battery that they want to give to me? because I already have a new one that’s fully functional. I want my refund and our relationship with this brand over.