Closed the account and i am still receiving calls from MBD.

I opened an account with Mr Price in 2016. Then in February 2018 i closed the account. A year later i started receiving calls from MBD legal collections saying I've been handed over to them and that i owe Mr Price Account. I told the agent that i closed the account and they said i should go back to Mr Price and Mr Price should send them a proof of payment and that i have settled the account when i closed it. Went to Mr Price and explained to them that i am receiving calls from MBD and i closed the account so they saying they want proof of payment for the account. They said my name doesn't appear in their system, their system clears after a year and the forms that we fill when closing the account they are throwing them away after a year, but they called Mr Price head office to enquire about the account they said my name doesn't appear in their system, so they called Mr Price mobile they said the account is closed so they don't understand why i keep on receiving calls from MBD. MBD kept on calling me time and again. I went back to Mr Price they kept on telling me that there is nothing they can do cause my name doesn't appear in their system and they always give me a number to call(MBD number) but whenever I call they don't pick up the calls. MBD agents are still calling me even now and some of them are even rude. So i dont know what to do now cause i don't get help whenever I go to Mr Price and MBD says they want proof of payment from Mr Price so that they can stop calling me. So what do i do now cause I've been going to Mr Price but i don't get help?