State Taxes: Correcting California Ftb (Income Tax) Error

I submitted my 2016 CA state income tax on time expecting a $3800 refund. However, I got a notice that I owed $1300. In their computation, they clearly made an error but I have not been able to get them to correct it, now after 7 months of trying. In CA taxes there is a form that shows whether income should be added or subtracted from the income that appears on the IRS return. I put in my social security pension payments, about $27000, as a subtraction since it's IRS taxable but not CA taxable. Their reviewer changed the minus to a plus. That resulted in taxing my ss pension not once but twice since it's already in my IRS income. I called and explained and they said, yes I see the error but we don't have your form schedule 540 which shows the differences in income. Now, I must add, this is not the first time the FTB has lost my return or part of it and it is always been a big deal to get them to acknowledge that they lost it, even with absolute proof, like they cashed my check one year but said I never submitted my tax return. OK, back to now. OK, I mailed the form to them but wasn't smart enough to do it with a delivery signature. Next call, they said they never got the form even though I mailed it and even sent it via my account on their web page. Next, an internet chat, the person complained that the form he saw on the web page wasn't complete, although it did have the social security amount clearly shown and the source. All the rest of the form is redundant. Social Security pensions are not taxable to CA. Next call, at the request of the representative, I sent an entire resubmitted tax form with all the changes they wanted to the (socalled lost) Sched 540 and also at their request a copy of my federal return. I sent it via fax from a FEDEX office. I have a receipt showing I sent it. The next call, they said they never received the fax even though I have proof and it contained my confidential tax records. They lost them. The rep said send another copy by certified mail. I did that and they are still sending me threatening letters. I mailed the forms with a signature return two months ago. Since they owe me $3800, I didn't think sending in the forms again would cause a problem even though it might appear to them to be late. After 7 months of many calls to them, I give up on trying to get them to fix the issue. The last rep I spoke to, I asked him, do you ever think you can collect taxes on my social security pension? He said no, but then nothing got fixed.I think that I may have to sue them to get them to send me my refund. How does one go about that if it comes to that? I requested help from my assemblyman. The last time they lost my return, the previous assemblyman's assistant got them to finally stop harassing me since I had the cancelled check proof they had received it and I had sent them a copy of the return. Then they wanted interest payments! Even though I had proof I had paid: The cancelled check.

State Taxes: Correcting California Ftb (Income Tax) Error