Unfortunately, I called Customer Service earlier today to request blocking a number in Ghana, but was told that they can't block international numbers.
If anyone reading this was (or still is) going through what I am, I feel your pain. I've been receiving up to 30 calls in an hour and half at all hours of the day and night. It started when I answered the first call and tried to be helpful with what I thought was a wrong number. I haven't answered since - 48 hours and hundreds of calls later.
What has made it more bearable is that I made the number a contact, assigned it no ring tone, and turned off the missed call beep. That way, at least, my phone is quiet except for when other people call. I'm hoping he will give up eventually, but if not, I'll have to change the number which I have had for years.