harrasing me at work

I get a call at my work place from a lady doing account for game RCS. She was rude and didn't have any of her information correct i have been constantly corresponding with game contact center and informed them in January that i am in financial constraint and would like a payment plan .They have agreed and i have been making payment since then as promised so you can understand my shock when i get a call of harassment at work stating that i never spoke to any consultant and there is no record what so ever on my file.I ask her why she hasn't called me on my cell as i am busy at work.She states that she has called me and left a message a few minutes ago .I tell her that my phone is right here in front of me she then says i have given the wrong number.Keep in mind i get statements from game .I told her that it is a inconvenient time and at my work place its not private if she could call me on my cell and she responds saying no she cannot call me and there is a charge of R19 a call.I am in a room full of colleagues and she keeps arguing with me saying who gave me a payment plan and claims that i am lying!!!what a ridiculous way to go about business.I work in account this is ridiculous !