Promo game won but did not count

Hello there. This is my first time posting on the forums, I hope I am at the right place.

I 'am' a rank Silver 4 player. I finally reached to 100 LP, and the system told me that if I win my next game, I will rank up. So I joined a game, and won that too. Yet I am still Silver 4. Can I please get some help regarding this issue and get it fixed? I am afraid to play more games because I might lose LP despite the fact that I deserved the promotion.

Thank you in advance.