Unscheduled scan keeps starting

I use the latest version of Avast Internet Security with Windows 7 64 bit. My problem is that I’m unable to delete a scheduled scan.
For many months I had a quick scan scheduled for every day at 20.00. Then I decided to change the time to 19.00. I changed the settings and my quick scan duly starts at 19.00. The problem is that then it starts again at 20.00 in spite of settings having been changed and no other schedule being set. I have no idea how to permanently cancel the old schedule. Any suggestions?

Go to the settings of scheduled scan and remove the checkmark in front of it.

Thank you but it’s not an answer to the problem. Perhaps I wasn’t precise enough.
The trouble is that the only scheduled task now is to be started at 19.00. There’s no scheduled scan set for 20.00 in the settings but it starts anyway.

Got the latest version installed ?
https://forum.avast.com/index.php?topic=166883.0

Your question is very clearly in the topic:

How to delete scheduled scan?

Yes, my version is up to date.
You’re right, the topic wasn’t clear enough. I’ve changed it.