been give very long number ma (about 24 digits)
That would be the bank account number of the utility provider. You should put PL, the country code for Poland, in front of it when making the transfer. That's the IBAN, the international bank account number. Depending on your bank's software you may need the swift/bic code as well. You can look it up here:
You also need the name of the utility provider eg Innogy or PGNIG or whatever company they are.
Ideally you should get the number of the 'Faktura' (the bill) and use that as your reference when making the transfer but if you don't have that you should use the customer's utility account number. It's really better to have the Faktura number though.