It sounds like you just dont have any pace on your groundstrokes. you may want to work on that for the future.
For right now though I suggest you learn to hit deep lob returns. they have to be high enough to get over the person at the net, and should be landing about halfway between the service line and the baseline. If you can put some topspin on them as well it will help to push them even further back after it bounces.
Völkl PB10 Mid with some strings at some tension