If the service provider is not providing their part of the contract, then they are in breach of contract.
You are naturally entitled to hold them liable for their part of the contract, and if they fail at their part of the contract, you must declare a breach of contract.
Keep all communication in writing only.
Once a breach of contract has been declared, and you have proof of the breach on their side, you hand in the hardware that is part of the deal and get somebody to sign for it.
Then you cancel the debit order from your side.
Later on, when you get threats from them, ask them where you can email / fax the details of the breach of contract to. Keep proof of sending the fax / email.
If you get any further request / threats from them, refer them back to your first fax / email, and tell them that you have proof of that communique, and the only correspondence that you will accept is correspondence that is a continuation from that previous correspondence.
If they are not in breach of contract, or you cannot prove breach of contract, then try to sell the contract to somebody else. If that fails, then you will have to negotiate with them 1 on 1. The difficulty in the negotiation process is getting yourself in front of a person with the authority to negotiate.
2 years is a really long time.
Why do people not think before they sign up for such a long period of time?