6a's don't have wireless charging.
If you can't get anything other than the charging icon, I suspect that would be because the low-level software doesn't want to try booting the OS until the charge exceeds some baseline level. If the battery never hits that baseline level then you may be permanently unable to boot.
Since you are getting the same results with various chargers and cables, I suspect you have a hardware failure. Maybe it's just a bad battery, or maybe it's a bad something else (I don't know where inside a 6a the battery-management decisions are made). A bad battery would probably be the best case, and it doesn't seem implausible given the symptoms you describe.
If it were mine I would probably be taking it to a repair shop, because I'm not DIY with respect to phones. Depending on when you bought your 6a, it might well still be under Google's warranty. There is some recent discussion here about repair shops, factory reset, and/or divulging your PIN/passphrase.
I hope some of this information is useful to you. Best wishes! If possible, let us know what you find out?