Have you checked with your teammates? If they have their names in the game and you don't, it is likely a clerical error and you should notify your supervisor to get it corrected. If neither you nor your teammates have their names in the credits, it is likely that it was decided at the contractual level and is above your pay grade.
Usually the external contractor submits a list of credits to insert for them. The names that appear in the credits for external contractor teams depend on the terms of the contract your employing studio has with the publisher of the game. If the contract terms say that all of the QA team must be in the credits, then you should be in the credits. If there is no such requirement, your name probably won't be. It sounds like the contracts your employer has with these publishers doesn't require all of their employees get credited. If that is the case, if having your name in the credits is important to you, you should consider looking for employment elsewhere. Your current employer may not be willing to put their workers' names in the credits.
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