No, AESA is under no obligation to respond or send any acknowledgement of receipt of your statement. 

However, the owner or person responsible for the maintenance and maintenance of airworthiness must keep the proof of the notification as proof that the notification has been made. 
 
If due to the impossibility of carrying out the online procedure, the declaration has been submitted by 

In general terms, a Declaration of Continued Airworthiness or an application for the issuance of a NARC may be submitted by the owner of the aircraft. In the case of multiple owners, this may be done by any one of them.

If the Declaration of Continued Airworthiness is signed within three months prior to the expiry of the NARC or the previous declaration, the pattern shall be maintained and the two years shall be counted from the date on which it was due to expire.

See graph below:

For AFIS aircraft, the Declaration of Continued Airworthiness may be signed up to two years from the end of the validity of the NARC or, if applicable, of the previous declaration. After this period has elapsed without being issued, the validity of the NARC may not be renewed by the NARC and the owner must request the issuance of a new NARC from EASA.

No, the new owner is not required to issue a new declaration.

Following a change of ownership of the aircraft, the NARC N15a or N15b signed by the previous owner shall be considered to remain valid until its expiry date.

There are currently no fees applicable for the declaratory renewal of the airworthiness certificate of an amateur-built aircraft.

This regime applies only to ULM aeroplanes of "Category A" as defined in Article 1(2) of Royal Decree 765/2022 of 20 September, which do not have novel or unusual design features, meaning those not covered by certification specifications or industry standards previously recognised through acceptable means of compliance by the competent body of EASA, and whose empty mass (excluding the ballistic parachute) does not exceed 120 kg and which are single-seater aeroplanes.