2007 Nissan Altima Child Seat Problems

I OWN 2 SUNSHINE KIDS RADIAN XSTL CAR SEATS. BOTH SEATS WERE PURCHASED AT THE SAME TIME AND ARE INSTALLED NEXT TO THE WINDOW SEATS IN MY 2007 NISSAN ALTIMA. BOTH SUPERLATCH BELTS LOOSEN THEMSELVES WHEN ATTACHED TO THE LATCH SYSTEM IN THE CAR. I AM APPALLED! MY CHILDREN HAVE NOT BEEN SAFELY SECURED DUE TO THIS! I HAVE INSTALLED AND UNINSTALLED BOTH SEATS MANY TIMES AND MAKE SURE THE SEATS ARE INSTALLED SECURELY EACH TIME. THE BELT THAT TIGHTENS THE SUPERLATCH HITS RIGHT AT THE BELT PATH AND WILL TIGHTENED WHEN INSTALLING, BUT LOOSENS EASILY EVEN WHEN IT IS NOT TOUCHED. I WANT MY CHILDREN SAFE! (RELATED VEHICLE INFORMATION: MODEL YEAR=2007, MAKE=ALTIMA, MODEL=NISSAN). *TR