Since you paid up front, likely the paperwork got pushed into a pile of "already completed" and while not likely, it looks like everyone dropped the ball on the ticket and they just parked it and waiting for you to pick it up. I guess fault lies in both corners on this, you should have called 6 weeks ago and asked why the work wasn't done and they should have better control of shop orders.
One other thing, you should have done the service yourself. You can do it all in a couple of hours and you would have become a bit aware of your tractor in doing so. I never understand folks who own a tractor but spend that kind of money to service it like an auto that you can drive into a business and leave 15 minutes later with services complete. Tractor owners should be capable and willing to do the minor stuff themselves. Surely in 2 months, one could find a couple of hours to do the work of an oil and filter change. Tractors are not throw away items that you use a few times and discard or trade in like autos. They are normally long term ownership items that owners dote on and love to work and tinker with. Just look at all the post where folks immediately start customizing their "baby" because they LOVE to work on it, take care of it and use it.
