The reason the credit is offered it is to compete with cable plans that do not charge extra for HD. If you want to get the credit continued, just tell them that [cable company name] does not charge it and you are thinking of changing...end of charge.
I again will reiterate that since this was Free HD for Life for new subscribers, us long timers are getting screwed. The only reason they gave it to us for 24 months was to placate us.
So, DirecTV, just eliminate it altogether.
FWIW, my last contact with CS was on behalf of a senior who bought a new TV and wanted HD contact. She is on a very restricted budget and we said she didn't want the extra charge...so they waived it. She's not a good payer and she doesn't have auto-pay; all I said was that the local cable company doesn't charge extra for HD and the monthly credit was added to her account.