No, "was" implies the past indicative, which means "If I was your cloud provider in the past", whereas "were" implies the subjunctive mood, which expresses "various states of unreality such as wish, emotion, possibility, judgment, opinion, necessity, or action that has not yet occurred" (http://en.wikipedia.org/wiki/Subjunctive_mood)

but the subjunctive is used inconsistently in english, and less so in england than in the usa. it's really not as clear as you assert.

I thought "If I had been" is past indicative, and "If I was" is ungrammatical.

Insofar as hodgepodgy English has real rules anyway...

"Had been" is the http://en.wikipedia.org/wiki/Pluperfect, further into the past than "was".