@BastiaanN
Hello,
Please try to reset the M7650 first:
With the Mobile Wi-Fi-powered on, use a pin to press and hold this button until “Power Off” appears on the screen to reset the Mobile Wi-Fi.
Then please create an APN profile as the instruction below:
https://www.tp-link.com/en/support/faq/794/
Kindly note that the APN information including APN, Username, and password, etc. are provided by your ISP.
If you put the SIM card on your mobile phone, are you able to get the Internet?
When you insert the SIM card to your mobile phone, please open a hotspot on your mobile phone, then use other devices to connect the hotspot. At this time, are you able to get a normal speed?
If you still can't see the 3G on the screen, please send me a photo of the screenshot, thank you!
May it help and have a nice day!