What are my options if I got the form 1095-C wrong and they don't want to correct it, and itis goig to affect my return because I had insurance with market place

The company that admin our payments doesn't want to correct the 1095-C, in spite that when I called them in July to  ask them if I could apply to the insurance through my employment, they say that I couldn't because I had to wait to the enrollment period and that would apply to year 2018. Then I kept my insurance with the marketplace and now they reported  that I had my insurance available since April. I'm not sure how that is going to affect my return. I talked to them but they said that they are not going to change anything. What shall I do?