A word or phrase for phone service working only one-way

This phrase should work for you:

You have failed to pay your bill, so your service is restricted to incoming calls only.

EDIT: As suggested by @Hot Licks, you can also use "inbound" instead of "incoming".

You could use the verb "suspend" to mean:

to stop (something) for a usually short period of time.

[Merriam-Webster]

You could say:

"The phone company (has) suspended (my) outgoing calls"

The technical term is "half duplex."

A full duplex channel has two way communications. A half duplex only enables one party to communicate at a time.

https://en.wikipedia.org/wiki/Duplex_(telecommunications)

A "simplex" is a strictly one way channel.

https://en.wikipedia.org/wiki/Simplex_communication