You can't, as explained at What happens if I get the same skill from both my background and my class? and in the Player's Handbook and Basic Rules.
However, there is a way to take a "double dose" of religion or any other skill as a variant human (or any other human, or a half-elf or half-orc). That is, you can take the Prodigy feat from Xanathar's Guide. This lets you choose an additional language, an additional tool proficiency, an an additional skill proficiency (following the same rules as above — no doubling yet). And it also lets you choose one skill you're proficient in and:
You gain expertise with that skill, which means your proficiency bonus is doubled for any ability check you make with it.
As a variant human, you can even take this at first level, instead of the Skilled feat. You don't need to "spend" the new skill proficiency granted by the feat on Religion, since you have it from your acolyte background — you can take something else. And then you can choose Religion as the skill for expertise.
If your character is human, half-elf, or half-orc, Prodigy is almost always a better choice than Skilled, especially if your DM is using the new rules for tool proficiency in Xanathar's. For example, if you have proficiency with Painter's Supplies, it's suggested that DMs consider giving you advantage and an additional benefit like extra information when examining religious artwork. In a party-based game like D&D, being really great at something is better than being middling-good at a bunch of things, and with 5E's "bounded accuracy" design, this kind of double-proficiency is hard to come by.
The rogue class has the Expertise feature, which basically does the same thing. But, you can't double these up for triple or quadruple expertise.