I dont know about the Cpl as where i worked there was a stray she had 2 litters of kittens before they came out and spayed her.It took endless phone calls to different areas but i got there in the end as i didnt want the kittens becoming feral, mum cat was scared but you could stroke her if you moved slow and had food for her.
I would give the rspca a call and keep a log of all the messages you send the owners Ex as this is proof they dont want the kitten.Surely they will take kitty and give it the love and care its in need of. Good luck