Premium increase a lot or no other insurance company willing to provide quotation mainly because 1. poor claim result, 2. no other insurance in the company, 3. the Insurer not willing to provide quote to "walk-in" customer. Besides using Broker/Agent to market quotation, risk management that mean work safety can help you to let the Insurer know it is a gd risk to take.
Bank of China Insurance lost a lot money last year in construction insurance, so they kick out these business in their portfolio since last Aug, other Insurers would take BOCI action as brenchmark to review the construction insurance, so they won't take new annual cover business, I suggest you could ask the current Insurer to convert arrangement to annual cover after a period of time