Today I moved from my Three provider to Vodafone. Initially I tried to O2 but credit check failed and did not recognize the Monzo sort code and account number. So it failed. Stupid because my credit rating is really good.
I went to Vodafone and there they did not recognize the bank with the sort code, so the credit check could have been not proceed. After they proceed the credit check it failed. And then i told them it is impossible! So I told them to call somewhere and fix it. After the other department did a manual credit check it worked perfectly fine.
That was my issues today with Monzo but finally it worked well
I just switched to EE but used my legacy account for the purpose of the credit check, once that was all through I switched the DD to Monzo prior to the first payment being due.
My Vodafone monthly contract direct debit has been coming out of my Monzo current account since September without issue. Perhaps they use different systems for new and existing customers?