If you're paying someone then I don't think its unreasonable to pay again after that time as they have to earn a living and getting rid of moles isn't an exact science as they can come from other property and generally be hard to eradicate.
I had to help get rid of loads that took up home in my parents garden and caused a right mess over a large area. We used traps and smokes for over a year but never completely eradicated them until we got so desperate up we used a ridiculous amount of petrol poured as quickly as possible through dozens of holes and then lit it from a distance. It was so effective it even blew up the runs across the garden as well but it was job done!
Not something for a small garden with nearby neighbours in case runs go into their property but that wasn't an issue. I still look back now and laugh at how we started so subtly but ended up going full Rambo!