iPhone 10x max dtmf tones

I noticed this problem today on my iPhone XS when calling a support line. I then tried calling myself on another line and cannot hear any DTMF tones coming across the call from my iPhone. I can hear them coming from the iPhone's speaker.

I have tried the following:

• rebooted

• confirmed that my other line's DTMF tones can be heard on the iPhone

• disabled cellular data and wifi calling

• disabled cellular data and wifi calling + reboot (cellular data keeps turning back on)

• toggled the ringer switch

• reset network settings

• disabled cellular data and wifi calling again