De jure the PCN is dead. De facto, the bozos at York haven't updated their systems.
Personally, I don't see the point in 'complaining' based upon them not responding within 56 days. You don't need their confirmation.
(7) If the enforcement authority fails to comply with the requirements specified in paragraph (4) within the 56-day period—
(a)it is deemed for the purposes of these Regulations to have accepted the representations made by the recipient, and
(b)it must—
(i)cancel the relevant enforcement notice,
(ii)refund any sum paid in relation to it, and
(iii)serve a notice on the recipient informing the recipient that the enforcement notice has been cancelled because the enforcement authority failed to serve a decision notice in accordance with paragraph (4)(b).
The law has deemed the PCN dead. Your complaint is that they haven't written to to confirm that something which the law has deemed to have occurred has.
Why are you bothered?