samsung - item found too poor quality

i bought samsung m** for my mother * months ago.every time i ring her she miss my call,i felt something wrong with phone,so i took a look what i found is its slow loading even for default apps ringing volume too low,i tried reset hard reset,this is not the first time i am using samsung but this feels strange to have a new phone which used to hang everytime u try to open,it in built with *gb ram and performanance is very bad.hope i get some solution here