Can't get a security notification on my phone

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So I am trying to set up my account and when I try to add a deposit method it tells me

For your security, approve the notification sent to:

Mobile number

and it is my phone number and I have received many OTPs on it and it works fine but it is not working for the notification I don't know why.

and I have talked to many agents and they couldn't resolve it. they even asked me if my carrier was blocking short codes and I checked and it was not blocked it works fine.

what should I do now? please I need this resolved ASAP