Poco — Motherboard dead again

My phone was dead 1 time then i submitted to service centre, and to solve it but they didn't solve it properly, it still keep shutting down on its own and i even go back there to repair this problem but they keep my phone with them and never solve it, and now few days later it is dead again, not giving me refund, not doing good service for their customers, not providing me new phone, fully disappointed 😞