It is very hard to find a stud service, and even more difficult to find one that will not rip you off. With artificial insemination, this is very easy for them to do.
I would continue to call around locally. Find one that will not only allow you to be present during insemination, but talk to them and get to know them well before you breed.
Breeding any other type of dog is nothing like breeding bullies. NOTHING like it. So it is important that you develop an excellent relationship with a breeder of bulldogs, so they can mentor you through the process. It is so important. So you are at the HARDEST part. Finding a trustworthy, helpful breeder. Do not go with a "stud" for hire. Go with a breeder.
It is very scary anyway, no matter what breeder/stud you choose. Trust is always going to be an issue in the bully world unfortunately, because so many breeders are in it for the dollars and not the bullies.