Part of the problem with these new valves is that it's hard to see where the
water is overflowing from. It could be due to overfilling but it's also
possible that it's the flapper valve mechanism not reseating properly.
Try and establish if the flapper valve isn't reseating properly (usually a
bit of jiggling by hand will get the flap to drop down again if it's
sticking) or whether ther water is going over the top of an "overflow"
straight down into the pan. If you can see it over-topping the overflow
then it's your fill valve that's faulty.
They seem to be susceptable to small particles of grit so simply (well, I
say "simply" but it rather depends on the valve and access) disassembling
everything and cleaning may sort your problem.
Sometimes replacing the whole shebang is just simpler and quicker.
Tim