Samsung
Turn a SIM Card On or Off auf Samsung
On a Samsung dual SIM device, each SIM slot has its own on/off toggle inside the SIM card manager. A system update, a factory reset, or an accidental tap can flip this switch without you noticing, leaving one number silently offline while the phone still shows a signal on the other line.
To check and restore the connection, open Settings ➔ Connections ➔ SIM card manager. Tap the SIM card that looks greyed out to reach Turn On/Off a SIM card, then confirm with OK. The slot switches from disabled back to active, and calls, texts and mobile data on that number resume within a few seconds.
If the SIM stays inactive after this step, the physical card itself may be damaged, misaligned, or blocked by your carrier. Reseating the tray, testing the SIM in another phone, or contacting your provider helps rule out a hardware or account-side issue before you assume a software fault.
Turning a SIM off deliberately can also save battery or stop roaming charges when you travel with two active numbers. Remember that a disabled SIM cannot receive emergency calls or texts, so switch it back on before you need that line again.