S5 Mini Disapointment

I am very disappointed with my S5 Mini. <br> Still under warranty, been for many repairs, and still i can not make a phone call that will last for more than a minute before the call gets cut.<br> I have explained this to your repair centre so many times, yet each time the phone comes back, it still has the same issue, and i am still paying for a contract which i cannot utilise fully.<br> <br> What do i do in an EMERGENCY???<br> <br> Please help me!