What happened to 30 days notice?

On 07 April 2020, I gave 30 days notice to cancel a Telkom cellphone contract. The person passed away. The contract was on month-to-month contract. Telkom billed me for the month of April as well as a pro-rata rate until 07 May 2020. Great - I am happy with that. Today, the number was cancelled and deregistered. Huh?? The reason I gave 30 days notice and agreed to pay the bill is because the minutes and data could have been used until 07 May 2020. Now what now??? This is unacceptable service and I must say, TYPICAL OF TELKOM! No wonder you are rated as number 41 when people must choose a telecommunication service provider...