Not sure I fully understand your query. I assume the letter you received was asking you what you would like to do with your fund ,i.e. do you want to transfer it to an company pension scheme with a new employer, do you want to leave it where it is, do you want to transfer to a retirement bond in your own name or, if you are in the scheme less than 2 years, do you want to take a refund. I assume that the contributions are all paid correctly up until the date you left the previous company, if so, then it's like any investment product really. Until you decide what you want to do the money stays where it is and has the benefit of gains or losses of the fund it is in, until such time as the fund is transferred out to somewhere else. The new provider can only invest the money on the date they recieve it.
Hope this helps.