Users with T-Mobile/Mint/Metro PCS unable to get through IVR Options on Landline phone system

I work for an enterprise with about 600 users. For almost 2 years now, we have been having issues where wireless callers from T-Mobile/Mint/Metro PCS and all of their MVNOs, have the inability to get through our IVR system. They will push options in our main auto attendant IVR and it will not register anything they press. Sometimes it will take 10+ calls before finally, they are able to transmit tones. I am able to duplicate this issue on my T-Mobile test line (signed up for the 90 day evaluation). Wifi calling disabled, strong LTE or 5G signal. Issue happens all over our City, and some of the surrounding cities. Iphone 14 pro max, all the latest iOS and Carrier updates. Our support vendor for our phone system and our SIP carrier keep telling us the issue is on T-Mobile's side. I have been working with T-Mobile support the past several weeks, and they tried to blame the issue on iPhone, stating that ever since iOS 13, the DTMF Long tones are no longer a thing, and to verify that our system can handle short tones. I don't buy the DTMF thing, because why would Verizon and AT&T iphones not have any issues with our IVR. They have now proceeded to kick the can down the road and told me to have our patients reach directly out to their support. Ok, we have done that, for 6+ months, and it got us nowhere, except 100s of angry clients with T-Mobile. What is that even going to show them?

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I am literally at my wits end with this issue. Does anyone else out there have a similar experience or issue? If you did and solved it, please tell me what you did so we can try it. We have tried the whole Network reset, Wifi calling on and off, etc.