Is there a cron-like service that fits this description?

Hi Everyone,

This is my first question here, hope you all are doing well.

So to describe my question, I am right now getting a couple of projects off ground and I am wondering if there is any service online available which does the following sort of workflow:

1. Our application sends a request to service with a payload (that may include certain identifiers and CRON like field which will specify the time)
2. The service acknowledges our request and creates a job (that runs on the schedule specified)
3. The service invokes a webhook (that we would have specified in step 1 when the job time is reached along with the payload that we sent in step 1).
4. We have an identifier for each job and We are able to cancel jobs based off certain events.

Example 1:

A new user registers, we send a request to the service with users details and ask the service to call back on a webhook after 7 days.
When 7 days are passed the webhook is invoked by the service with user data so that we can do further actions - like sending a second email to user OR some other stuff.

Example 2:
We ask the service to call back a webhook at fixed intervals (like every 30 days) with some custom payload that we configure when registering the job.

I did look at EasyCron but I don't think that fits the needs.

We could also build something on our own but I am trying to avoid some development effort right now.

Zapier is another option but because of the estimated volumes it is going to cost a lot (I am looking for something cheaper). and also I was not able to find if a zap can be cancelled.

So has anyone of you used such a service, if yes would you recommend anything?

thanks and regards