It isn't up to you to prove what the Bank did with the money thereafter, as LEY 57/68 states that it is for the Bank that first received the deposited monies is required by law to make provision for safeguarding those monies into a secure safeguarded developer account. That is the whole purpose of Ley57/68 to ensure that inalienable protected rights are adhered to according to law.
What nonsense to suggest that you are responsible for what a Bank does with those monies thereafter. This is the whole purpose of Ley57/68 for Banks to remain accountable for correctly administering and safeguarding purchasers deposited monies from the outset.
So long as you have proof of payment to your lawyer and your lawyer can prove that monies were transferred to the developer account ( presumably this is proven via the developer's receipt of same) then that should suffice as far as your responsibilities were concerned.
Innocent purchasers should never be made accountable or scapegoated by Banks not adhering to the letter of the law, a law intended to protect in the event of developer insolvency, contract cancellation etc.
This form of ruling if not careful sadly appears as interference intended to protect the Bank, by failing to recognise the essential Banking administrative procedures as set out in Law Ley57/68 to safeguard offplan deposited monies until such time as the contract is honoured.
Appeal judges and Supreme Court need to reflect on this, as to turn blind eyes to this implies that the rule of law which states that everyone is entitled to protection and legal certainty according to law is at stake here.
To remove an essential element relating to legal certainty in this way undermines the very basis upon which law is enacted, and also if not careful undermines another essential principle to the rule of law, that of judicial independence free from interference of any kind.