Self Assessment application keeps getting rejected to due address error

I'm trying to register for Self Assessment as I am going to be hired as a consultant for the first time, and I am under the impression that I need to include an UTR number on the invoice that I provide them. They have a deadline for spending so I really need to get the UTR number asap. But every time I submit my application I get an email back complaining: "We are unable to process your application because the address provided does not match our records." I have checked a million times and the address I am putting is exactly the same as the address on record. What can I do? I have no idea how to reach someone who can actually help and fix this.

Hi,

If you are still getting the error, you should contact our Income Tax team to advise that you are unable to register online:

Income Tax: general enquiries

Thank you.