Phone faulty

I bought a OPPO A40 on the 13th of February ,It gave me a problem from the word go, speaker , people can't hear me,I sent it back to Truworths they sent it to MTN, , MTN brought it back and said nothing is wrong yesterday i took it back home, still no luck speaker still a problem,I need help please am paying for this phone, its 2 months now without a phone but am paying.