No need to use sudo there and I’m not promising that above command might work at all, yet it needs to be changed to resemble this one:
mmcli -m /org/freedesktop/ModemManager1/Modem/0 --simple-connect="apn=internet.myisp.example"
Also, this .xml file might be the most recent, related one in order to find telia related settings: https://github.com/sailfishos/mobile-broadband-provider-info/blob/master/mobile-broadband-provider-info/serviceproviders.xml.
For example Fello uses online.telia.se, as described here: https://forum.sailfishos.org/t/wrong-service-provider-settings-for-fello-sweden/11329.
As well and at the first place you might choose or even need to follow this (most recent updates related) Linux path: How will APN settings work?.