What should I do about the failure to cancel my subscription to the forbidden health insurance, and am I sinful for that?

If you have exerted your utmost to cancel your insurance subscription but were unable to do so, then there is no blame upon you; as Allah, the Exalted, says: "Allah does not charge a soul except [with that within] its capacity." And it is permissible for you to benefit from this insurance if it pays you an amount equal to what you have paid or what the company has paid for your insurance.