Formal:
* Contacted
* Reached out to
* Communicated with
* Engaged with
* Made contact with
* Checked in with
* Pursued
* Inquired about
* Verified
* Monitored
Informal:
* Got back to
* Checked in
* Got in touch
* Heard back from
* Got an update from
* Got a response from
* Heard from
* Reached out
* Got a word from
* Followed through with
Specific to a particular action:
* Reminded (if you were reminding someone of something)
* Requested (if you were requesting information or action)
* Confirmed (if you were verifying something)
* Responded to (if you were responding to something)
The best synonym will depend on the specific context of the situation.