Any Unknown or Unlisted Aircraft Manufacturer
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Flight Instructor
Flight Crew Last 90 Days 30; Flight Crew Total 18200; Flight Crew Type 820
Communication Breakdown; Situational Awareness
ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Environment - Non Weather Related; Human Factors; Procedure
We were training and went to ZZZ to use their ILS (in VFR conditions- no flight plan). After the approach; we did a few patterns and departed for ZZZ1 (about 18 miles). ZZZ asked if we wanted flight following and we agreed and entered a code. We departed north east to ZZZ1 and told them we would be operating west of ZZZ1 in our approved practice area. There was no further communication with ZZZ and due to the lack of activity with COVID there was absolutely no communication on the frequency. We forgot about them entirely and headed back into ZZZ1; forgetting to 'cancel' flight following. (There was no call from ZZZ to terminate either). On the ground Tower asked us to call and informed us of a 'possible pilot violation' and upon talking with ZZZ we were told we forgot to cancel radar services. There was; in fact; no traffic at ZZZ or at ZZZ1 at the time and no separation was lost or diverted.I think the primary cause was the complete *lack* of traffic. We never heard a call on frequency for a half an hour and while conducting our maneuvers (a busy time) we forgot entirely that we were being monitored by radar. Our last maneuver was an 'emergency descent' and we were pretty quickly in ZZZ1's airspace and never 'canceled' flight following with ZZZ.
Pilot reported they were advised by ATC they forgot to cancel VFR flight following.