I have just installed a Recaro Proride in our 2011 Lexus RX350. After connecting the latch buckles, the manual says to pull on the loop end of the latch belt to tighten. These belts will not budge to allow me to tighten them. My husband tried also, still won't tighten at all. Any suggestions? I'm assuming we either installed wrong or are doing something wrong in general. Thanks!