How many phonecalls do they want to make

I had a bad incident where I had to make arrangements to repay all my accounts. I made an arrangement with Edgars who did not accept the arrangement and handed the account over to VVM for collection. I made exactly the same arrangement with VVM which they accepted but without fail I get up to 7 phone calls per day about twice a week on this account and the biggest problem with this is that I get charged for every phone call. I made the arrangement, I stick to the arrangement every single month yet they have to phone me 7 times in one day. Why would that be?