Ah. then you might be able to recover the situation.
It would help to know the make and model of the r9uter. I have an old TalkTalk one that has a label in the back. Top left, it says model number HG633.
Beneath that it gives two barcodes. One is the Wirelessnetwork name. The other is the Wireless password.
We're not interested in those, because you said they were changed.
At the top middle in smaller type are four lines:
Default router settings
IP address 192.168.1.1
Ruter username: admin
Router Password: XXXXXXXXX
If you have a similar label, you may be able to log into the router and reset the wireless network password.
Procedure:
1. Ensure the router is switched on and connected to the network
2. Go to your browser and enter the IP address given (eg 192.168.1.1)
3. log in using the credentials given (admin/XXXXXXXX)
4. You will then have number of options, including re-setting the SSID and Network password.
Good luck