word choice - Is there any difference between "my level of English" and "my standard of English"?

Is there any difference between both sentences? Are they synonyms? Is one better for formal speaking than the other?

Recently I was rejected in a job because

The standard of your written English is not at the level where you could write a report to our standard.

I'm trying to figure out what is the meaning of standard in that sentence, and I came across that standard also means level,

Answer

It's quite true that both level and standard can be regarded as synonymous. However, there is indeed a subtle difference between them.
Suppose there is a competition where there are ten levels (ten rounds; you can participate in a round only if you qualify in the preceding one). Now, there can be different players in each level. However, the standard of the players in each level differ. Agree? As in, the quality of players in each level are different. In level 8, there can be player who has just luckily cleared the seventh level. Also, there can be another player who plays extraordinarily well. This means, the standard of this player is way better than the former.
So this is where the difference between level and standard lies.
However, based on context, you can use either of them for the same purpose.

As regards to you being rejected from job, I think your boss just wanted to tell you that you don't write good English (according to him). Simple.