Okay I think there are actually two questions here.
1. It can take MONTHS for publishers to get contracts to writers, which I find frustrating especially since many advances are paid on signing. But that comes down to all the red tape publishers have to deal with all the different people who need to go over the contract. In your case since you'd already got the contract and signed it, it shouldn't be as big a deal because they only have to sign it. But still, contract stuff, I have found, in almost all businesses, are a slow slow process.
2. You say you had very good communication up till now and they aren't returning your emails and phone calls. This to me is a bigger deal. Right now, at a week, I wouldn't worry too much about it. After all you have now signed a contract so they aren't now going to lose you, they can relax, they don't have to butter you up quite so much anymore. However, there should still be respect and they should still respond to you in a timely fashion. I'd say if another week passes and they don't get in touch, that is something worth getting concerned about. Again, I'm not talking about the contract. I'm talking about the respect an editor gives their author. After all, you are now a team and you need to trust that they will communicate with you in a manner that isn't like pulling teeth. So yes, I'd say their radio silence is a bit of a thing. Right now? It's not a huge deal. But if it lasts? I'd get on that. You don't want to start a precedent where you never know what's going on, where they only talk with you when they want to, etc.
ETA: I want to add, poor communication skills doesn't signal a scam or anything, I don't mean that you need to be concerned about that. I just mean concerned about the quality of the business relationship. I've worked with small publishers and big publishers, and while there has been many slow parts (getting contracts, getting edits) email communication with my editors has always been straightforward and easy. But I do have author friends who found communication with their editors extremely difficult, and it just made the process unpleasant and very frustrating. And honestly I think we authors need to expect better and to be treated professionally.