Lenovo — Lenovo laptop working extremely slow for long time

I have purchased a lenovo laptop through lenovo's online registered site on 14.06.2021. The details of laptop are as below

81VD00EFIN- IdeaPad
S145 39.62cms -
Platinum Grey
Serial No:-PF2VWWF3

The laptop became defective after sometime and could not even turned on. The same laptop was given for repair at lenovo service centre, rajkot, Gujrat, since it was under warranty for 1 year. After repair it was informed that the laptop mother board was defective and they changed it. After repair it was found that laptop was working very slow and it was again taken to service centre but service centre denied accepting flaw at their end. They refused to attend the complaint again and only said problem not from their side.

I hereby humbly request for changing of my product i.e. laptop not repair of any component to avoid any further problem.

If it is not possible then I should be given full refund as per invoice.