Disappointing service from Bonitas and PMB department

Almost two years ago my depenedent went for surgery. Only now do i get a satement for almost R20 000 that Bonitas failed to explain that it is owed by the member and now the dr is harrasing me for this amount. And its been almost a month since i asked for my withdrawal letter/ last membership certificate. I was a member for almost 5 years this is so disappointing. Even Dr office confirmed they have had zero luck in getting through to PMB to pay the outstanding balance.