Do not ignore the Order for Recovery or lose time trying to talk to council.
If Mum hasn't received the NOR then fill in the form, ticking the appropriate box, Mum must sign it, email to TEC (details should be on it)
Don't trying to argue the case on the form or add any information bar the basics above.
Once TEC receive, they will cancel the OfR and Charge Certificate (which also seems to be MIA) and tell council..... authority will then refer to Adjudicators.... though likely to send a letter to Mum with a copy of the NOR and an invite to pay