Hello @Juanjo43757 ,

According to Google Translate, your question is: after switching phone companies, you're unable to log in to your TP-Link account for your RE200 Range Extender because you deactivated the device, and you also can't change the Wi-Fi network name to boost the signal. If there is any discrepancy, please describe it in English.

For the TP-Link ID binding :
If your extender says that it's bound to another TP-Link ID (which may have happened when you deactivated it), you can try performing a hard reset on the device. 

For logging into the extender:
If you're having trouble accessing the extender after the reset, try these steps:
1. Make sure your phone is connected to the Range Extender's Wi-Fi properly. If your phone is connected to the host router instead, you won't be able to access the extender.
2. Try using the IP address of the Range Extender instead of the domain name. After a reset, the IP address should be 192.168.0.254.
3. If you cannot log into the extender via the Tether app, try these troubleshooting steps: How to remove existing wireless network profile on Android&iPhone

• Try logging in using another smartphone or tablet to determine if the issue is specific to your current device.
• Power cycle the extender by unplugging it for about 30 seconds, then plug it back in and wait for it to fully restart.

For changing the extender's Wi-Fi name:
Once you can access the extender, you can modify the wireless settings using either:  

• How to change the wireless settings of TP-Link range extender on the Tether App 
• How to configure wireless network on the range extender