Poor customer service

I contacted them in Jan 2019 for extended service plan on my vehicle to which was signed and sealed. When my vehicle had to be serviced in June, only to let me know that they never activated the policy. I had to pay cash for the service. That being said, now they are sending mails and messages to re-instate but I already paid for the service. I don't understand how such a large, established company can make this mistake...