I think you should be able to amend your payment details regardless of how much is in your account. The fact I had over £200 in there should not have affected my ability to obtain my funds, despite my payment method having expired. The first operative I spoke to was telling me to send lots of documentation including a bank statement and photo ID, in order to get the money. He was also not able to do the transaction himself but referred me to an email address. When I spoke to William, however, he did the entire transaction himself and was very efficient. This changed my view of Paddy Power greatly.