I doubt its a con pippin its just that the older you get the more insurance costs as the risk of a claim increases with every year you live, a 20 year old will get much cheaper insurance than you will and my insurance if I took any out now at 61 would be higher than yours is. Thats just the way it is, not a con.
Any insurance you have is best kept as you will never ever get it cheaper as you get older. Anyone trying to get insurance after a diagnosis of diabetes is going to pay more than a non diabetic as well as the risk of earlier death is increased.
So its not a con but any ins quotes are subject to underwriting conditions that are effected by age and medical history, if a company wants to discount their rates for a period for people such as diabetics then thats up to them but again even a discounted rate will be more the older you are.
Be thankful that you have some insurance already in place as many dont and once a diabetic diagnosis is given, often later in life as with most T2's, the cost can be prohibitive.