Will Bed
I get it as "getting the payment is now under the responsibility of Hydro" since you have done everything you legally had to do ... So they now have to honour their legal obligations too... They are responsible for it. They are SURETY for the matter of getting their payment. The music's still playing.
You served the ball back to them. You have honoured your responsibilities you are not responsible for the rest. If THEY fuckaround with this, THEY are the only ones responsible....
English and legalese aint my first languages, but it seems that : You understand facts, laws, etc. You undertake actions, procedures, etc.
When you underSTAND, you are responsible. When you underTAKE, you are responsible. Being responsible = SURETY.