Hi & welcome to TP
Firstly, lots of folk here use Loxleys and DSCL......but there are of course other labs.
But maybe a good idea to post how are you preparing your images to be printed I.e. why did the last lot come out too dark compared to the previous ones. Was it perhaps something you did or failed to do this last time.
But back to basics.........is your monitor calibrated? Note - a common reason for folk to report "prints too dark": is that the monitor is set too bright! So just a thought.