Any identity provider's automated system rely on Data Providers, Credit reference agencies, government departments and some financial institutions to Verify your identity.
What they look for is a well established and credible credit and financial foot print that link your Name to your Address.
Have your changed Name and or Address recently? if so when? (90 days ago or less?)
In which case you will have a better chance to Verify using your old Address, and or previous Name
It does take time and several transactions to provide such a strong credit trail under your new Name and or Address.
If all else fail, your best option is to try to Verify using one of the other certified identity providers, please see list below:
2. Digidentity (may not require a mobile device)
3. Experian (does not require a mobile device)
4. Post Office (can also Verify EU Citizens)
Alternatively, you can contact the government department direct for the service you require Stating that you were not able to Verify online