3rd time phone power button broke and client pay

hi<br> <br> i upgraded my contract last year september (2015) and took a Hauwei tablet. 2 weeks later the power button broke. after sending it away cell c replaced the tablet. 2 months later again the power button broke, cell c sent away for repairs and eplaced. in Dec / January this year (2016) again the power button broke. now cell c wants me to pay R855 to fix because there is a crack on the face of the tablet. i advised that i did not want the crack fixed and they should fix the power button but to no avail. please help as im still paying the contract and need my ph.