What compost did ??ou use? Ordinary mpc? Have you been over zealous with the watering? Over generous with fertiliser?
Just because you put slug pellets down it doesn't mean your plants won't be attacked. If you replant I suggest you inspect your plants with a torch and pick off any slugs n snails you see. Still use your pellets but, ironically, too many attract the pests. Just a few pellets is all that is required.
Sometimes mice and other small rodents will sever the stems,of some plants and there are other soil pests but snails are the likely culprits