M8 can't receive calls, flashed wrong ROM? (4G problem)

Yesterday I flashed my AT&T HTC M8 to a custom ROM (Wolla) because my phone was really laggy after the Lollipop update, and I noticed that although I am still able to make calls, I cannot receive calls anymore. I am wondering if it is possible that I messed up a step somewhere (especially step 3), or if I flashed my phone with the wrong ROM?

I also looked around on XDA more, and realized a few people also had this problem, and it was resolved by turning 4G data off. Apparently this is a problem with AT&T activating Voice over LTE, and the custom ROM not supporting/compatible. Is there a suggested fix to this problem (eg. flash back to the RUU on HTC's site)?

Here are the instructions that I followed to flash the new ROM:

1. Unlocked my phone via the HTCDev website
2. Installed TWRP
3. (Here is where I think the problem occured). I downloaded the Wolla Marshmallow ROM from the XDA thread, and took the boot.img image from the .zip into my fastboot folder.
4. Then in fastboot, I typed in "fastboot flash boot boot.img", then "fastboot reboot" to reboot my phone.
5. HOWEVER, my phone would be stuck in white Android booting screen, and wouldn't move for around 10 minutes, so I thought it was stuck.
6. I redid step 4 a few times, but the same thing always occured.
7. Finally, I decided to take the boot.img file from an RUU from HTC's website, and use that instead of the boot.img from the Wolla .zip file.
8. Now my phone boots, and everything seemed to work.

The only issue is that although I can make phone calls, I cannot seem to receive phone calls. It doesn't "ring" on the caller's end, and goes to voicemail in the end.

Does anyone have any experience with this?

My phone is an HTC One M8 bought from AT&T, unlocked about a year ago.

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