Pathetic Customer Service after 15 years of loyalty!

I've been with this company for over 15 years, renewing my contract every 2 years and the past year, I've been in credit with them, so in agreement with one of their consultants paid them half of current bill so that I don't pay the full account before the contract comes to an end. In January my account gets suspended so I call to find out why and was informed that they didn't receive a few payments and that they'll need Proof of Payment,. So I send them proof of payment and the response is they didn't receive the money their account. Funny, they've received every other payment but not the ones in questions and refuse to assist even though I've give proof that they've been paid. That's the service you get after 15 years of loyalty!!!!!!!