+1.
You are in the mire.
IMO, your only possible course of action is to write to the council NOW - the penalty is still @£240 so it's at the Charge Cert stage and an application has not yet been made to the court for an Order for Recovery- apologise and ask if they'd accept late submission of formal representations. Explain why they're late and submit reps as you did initially.
Otherwise, your minimum liability is £240 with an imminent possibility of an increas of £10 then ......
Wait for others.