T-Mobile is notorious for the blame game. Apple isn't sending your voicemail messages in text to you. T-Mobile.
Disclaimer. I'm not a T-Mobile customer. But I did do some research and I saw several T-Mobile complaints about this. I got this from a Google Search and I cannot validate it at all as again, I'm not a T-Mobile customers, be see if this helps you:
"To stop T-Mobile from sending transcriptions of voicemails as text messages on an iPhone, you can disable the feature through your T-Mobile account settings. Go to the T-Mobile app, navigate to the "Account" tab, select "Profile settings," then choose "Block calls and messages" and "Block Other" for the specific line you want to update. Enable the option labeled "T-Mobile Voicemail to Text Block" to prevent the text transcriptions from being sent. Alternatively, if you have the T-Mobile Visual Voicemail app installed, you can disable the transcription feature directly within the app's settings under "App Settings". Note that some users have reported that this setting may reset over time, particularly after account changes or updates, requiring reconfiguration."