Cellphone

I bought a Mobicel star on the 24 July at southgate mall, the lady that was assisting me informed that i have 7 days to return it if it happens that the phone freezes or it slow i , I went there yesterday 31 July and the lady that i found there did my days count and say i am still within my 7 days

She just need to call and get the OTP number for my refund to be processed, as she was taking so long she suggested that i should go and she will call me once my refund is ready , I then get a call to say that the Manager says my 7 days has passed on the 30th so i cant get my refund ,

I was given number to call mobicel and complain , Who has the contract with Mobicel to sell their phone? Why do i have to contact mobicel not the store

Why did the lady at first confirmed that I am still whithin my 7 days?

I am not happy with the service at all