In your IVR you can block callers and disconnect their inbound calls.

Go to your IVR where you want to block the number.

Add a Switch block to the IVR in the beginning of the IVR before anything else.

Give it these setting by double clicking the switch block.

Draw 2 outgoing line from the switch block, one to a hangup and the other to continue the IVR. On the one going to the hangup you can add numbers you want to block, to add multiple numbers use , between them. The standard is to add them in this format 46734567890

On the other line to continue the IVR add a -