[2021] Vbucks on different devices

So I have a quick question.. I have a Fortnite account on my PS4... And I changed it to an Xbox for a skin so the skin had 600 vbuck...originally I had like 1500 saved then in the Xbox it showed to be 2100 so I bought a the pig BB so it went down to 1700 then I changed it back to my PS4 and I had only 1100 v-bucks... Now the real problem is this... In Mexico The PS4 charges us around 10% tax for a purchase and on my cellphone the prices are cheaper could I buy the Crew on the cellphone and everything would go to my PS4 account or would it affect the vbucks... I'm sorry if it's not well explained... Hopefully someone understands me and helps me...