First of all, your pity has NOT been reset. Here's their official reply:
* Additionally, they also updated wish history to show up to the last 6 months instead of 1 month.
And now, a brief explanation of the pity system.
(Mainly because a lot of the confusion seems to come from people not understanding how pity actually works. And because of the misinformation spreading, some people are scared to roll.)
1. Promo/Standard banners- Hard pity at 90. Soft pity at 76+. Chances goes up from 0.6% to ~32%.
2. Each banner of the same type (ie. Promotional Character, Weapon, or Standard) has a SEPARATE pity counter.
3. Your pity counter resets for that specific banner type as soon as you get a 5*. It goes back to 0 and you start over the count.
4. If your last 5* was not the promo character, your next one is guaranteed promo. If it was the promo, your next 5* is a 50/50.
5. Pity counter carries over to the next banner of the same type. It does not reset.
Closing thoughts-
If after all this, you still think your pity's messed up, please do a recount. Also remember that hard pity is 90 and you're not guaranteed to get a 5* before 90. I feel you, but we really are that unlucky sometimes.
Mihoyo's decision to wipe the history page was a strange one, and I think they should've announced it beforehand in the patch notes or in an official announcement. In fact, I wish we could keep ALL of our wish history no matter how old. OR have a pity counter displayed directly on each banner.
(Also sorry in advance if this type of post has been made already)
Good luck to everyone rolling! Xiao pspsps
EDIT - I'll do my best to answer any questions you may still have after reading this whole post. However (PLEASE), read through the comments and replies in this post before you ask, because your question was probably already asked by someone else and already answered.
EDIT 2 - I'm turning off notifications from this post so I won't be replying to questions anymore! Tbh I got tired of answering the same questions over and over, and I'm not even hoyo staff lol... Anyway, PLEASE read the comments, because your question is most likely asked and answered.
Bottom line is,
- if you did not get a 5* (any 5* at all) on a banner type, your pity did not reset.
- If you got a 5* (any 5* at all), your pity is back to 0. This is the ONLY condition that resets your pity. Period.
- 3 separate banner types (Promo Character/Weapon Banner/Standard Banner), all have 3 separate pity counters. What happens in one banner does not affect other banner pities.
- Pity carries between banners of the same type.
- Pity does not reset no matter how much time has passed since your last pull. Didn't get a 5*? Pity still there.
Signing off 
your girl is tired
