As I said, MATS 1 is clear regarding the responsibilities of ATC with regard to over due action on radio equipped aircraft who have filed a flight plan.
S3 C1 suggests that an Approach Control Unit provides ATS (including an Alerting Service) outside controlled airspace when:
overflying aircraft place themselves under the control of approach control until they are clear of the approach pattern and either no longer wish to receive a service or are 10 minutes flying time away from the aerodrome, whichever is the sooner.
and within controlled airspace when:
overflying aircraft are within the relevant controlled airspace.
What leads you to believe that an Approach Control Unit owes you an Alerting Service merely because you send them a FPL?