double billing incompletely reversed and promised credits not yet applied 6 months later

(Here's the rest of the post due to character limitation to 2100 characters).  June 10th still no updates or credits so I opened a billing dispute.  June 16(today) the phone rang. By the time I got to the handset they hung up - call display said it was Telus calling.  Rang 1.5 rings.  Checked the support request status and see it was marked as "resolved" exactly when they called and hung up.   Opened another ticket.  It's now been 6 months since they double billed me and reversed the double billing incompletely.  They've closed 2 of the tickets as resolved when they aren't.  I've spent a whole day on the  phone over the noted calls above. The credits were supposed to be an acknowledgment for the "inconvenience".  I have paid what is owed after the last promised credit, but late charges continue to apply because the credits and charge reversal have not been applied.  How to get through to someone who can fix this once and for all?