How can a company buy the assets of another company without getting their liabilities?
Via Asset-Purchase Agreements. There's a few caveats, not limited to Successor Liability (wherein the operations of the business continue without significant change and so the liability transfers, irrespective of the agreement) and further paying a good faith price for the assets.
The original company
can sell just the assets and not the liabilities, but they remain on the hook for the contract. So the old company still is required to give you VPN services as per the contract or face breach of contract. I am however not sold on the fact that the price paid was a fair market value. As such the agreement may be found to be fraud.