when you put i together put the phone on unmute and make sure the silent switch on the case is the same then you put it in the case silent switch side first. (I was gonna include a vid on putting it together but in the interest of time i cut that segment.) Look for the instructional for the genuine case assembly though the instructions are the same. Thereafter it should be pretty impossible to switch it to either mute or unmute. Then just enable accesibility opptions and triple click your home button which will bring up a user panel to enable or disable silent mode right from your screen.
As far as the wifi, if its just slower on your gfs network but its equally slow there with or without the case on then its the network, but if youre sitting in the same spot doing the same thing and you try it with the case on and then try it with the case off and there are less signal strength bars then it would be clear that it is the case at that point. Check it out and experiment and post your findings because there could be some interference on different routers or perhaps different bands that have yet to be determined.