Most title companies wont touch wholesale deals unless it is purchased cash. Even then some will not because they are taught that wholesaling is illegal, which its not unless your involving financing, then it is. Title companies will most likely require all buyers to bring their own funds to the table, thus transactional funding was born..lol.
I do wholesales without using transactional funding b/c my buyers funds will close the deal for both parties. Some title companies still have an issue with that but you can get around it. There are a few ways around this if you do some research here on BP you will find em all.
I have never used an assignment of contract and had a deal go through so I don't use them. A standard real estate purchase and sales contract is all that's used to do the deal, not aware of any wholesale contract exactly. I sign one contract when I buy with the seller and a different contract with the person buying from me....that's it. I take them both to a title company and let them sort out the money details when my buyer gives them the $$ or my buyer pays me directly and I pay off my purchase then have the title company deed the property to my buyer. You can also use separate title companies if need be.
I would look for an investor friendly title company that's use to doing these types of deals also. The one you called probably just pushed you to the curb b/c you ask a newbie question (no harm intended) or dont know what a wholesale deal is so just find another one and start over once you have a deal.
You can download free real estate purchase and sales agreements from many different sites. For me, the shorter and simpler the better for all parties.
Hope this helps.