Can you provide some additional details on the VoIP service? When you say "parking it on a VoIP service" do you mean that you ported from T-Mobile to the VoIP service or do you mean you forwarded your calls to a VoIP line and continued to pay for T-Mobile?
Who botched the port request? You would have initiated the port request via US Mobile when you signed up for service. They wouldn't depend on T-Mobile "having the number", they would have looked up who had the number and initiated the porting process.
Now, if you cancelled your service BEFORE you ported the number, then you may be SOL as the number would have been released. Even if not reassigned you may not be able to get the provider/carrier to release it since it is no longer in your name.
I ported from VoIP to T-Mobile successfully, then tried to port from T-Mobile to US Mobile because US Mobile is $15/month. I did not cancel before I had the number.
Who botched the port request? You would have initiated the port request via US Mobile when you signed up for service. They wouldn't depend on T-Mobile "having the number", they would have looked up who had the number and initiated the porting process.
You can see which carrier "owns" your number by going to https://freecarrierlookup.com/.
Now, if you cancelled your service BEFORE you ported the number, then you may be SOL as the number would have been released. Even if not reassigned you may not be able to get the provider/carrier to release it since it is no longer in your name.