I'm unable to return to work because Lincoln Financial won't track my calls after claiming I never called them.

I was recently let go from my job of 7 years because Lincoln Financial claimed they had no record of me calling them when H.R contacted them. Since then I have called and spoken with several different people. After speaking to my plant manager he told me that if I can provide my case number and proof that I called them then he would make it right. However I’m still waiting on Lincoln Financial to track my calls! I’m in limbo and not able to return to work.