Can't receive SMS and OTP

I've been using the same MTN number for the last 10yrs and recently I have not been getting SMS and particularly OTPs on this number which is a huge inconvenience for me because I can't access or install a banking App and access social media profiles.

I have logged numerous calls on the 135 number and physically at the MTN stores with no success.

I don't think this is a unique issue and I'm sure MTN can resolve but now I'm not sure where to go anymore because I've done what's needed on my end and the issue is still not resolved 😭