bad service

Good day

I just want to report Identity for the poor service I've been getting from the time I've opened this account .I skipped my first payment by mistake they already handed me over to debt collectors .I paid my account up to date and still I'm getting sms's and when ever I want to do something it shows' the account is in arears nd still im getting statements after i have paid my account . That i still need to pay what i already paid what system are they using that can not update payments .This is the second month they are doing this