Visitors Insurance

I took a single insurance policy to cover my visiting parents where my father was listed as primary and mother as secondary. Since my father left the country early, I wanted to cancel only his insurance and leave my mother's untouched. I called IMG and an agent told me this was possible and asked me to request the same via email. I emailed IMG clearly stating that I needed my mothers insurance to be kept intact. I got an automated reply saying call IMG if you dont hear back within a few business days. I assumed that IMG had processed my request just the way they said they would. I called IMG 2 weeks after I got an automated reply to check when I would receive the refund for the cancelled policy. They then told me that they cancelled my mother's policy as well! I was furious when I learnt that my mother was not insured for a period of 3 weeks! According to their supervisor, they cannot cancel the policy for the primary alone.
My question to them
- why did they say so otherwise when I called them up
- why did they cancel my mothers policy without checking with me via email or phone when I have explicitly requested them to keep it intact. They have my contact information. In case my request cannot be processed as is, I expect them to check with me without taking such dangerious decisions like this.

I re-applied for my mothers insurance from scratch. Luckily, I did not need medical insurance the few days she was without one. But if something had happened, it could have been a financial disaster for me.