Letter of complaint check

Could you check this letter and correct mistakes if there are any?

Dear Sir

I'm writing to complain about the technical problems whichoccurred during our musical performance. There are somepoints I would like to mention.

I am quite dissatisfied with the music equipment that we were provided with along with the venue rental. Although I was told that the equipment would be of the highest quality, it turned out that we were given faulty and out of tune instruments. In addition to this, we received insufficient number of keyboards, accordions and guitars. Owing to this problem, instead of preparing for the show, we were forced to fix and tune up the instruments and, by extension, we lost valuable time that could have been spent on the last rehearsal before the concert. Consequently, not only did it cause considerable stress, but it almost ruined our concert.

What made matters worse was the fact that during our show, the main spotlight kept overheating and, as a result, the centerof the stage was in darkness.

I expect to see this problem problem solved as soon as possible. First of all, I would appreciate if you provided uswith a full explanation concerning malfunctioning equipment. Secondly, I would be most grateful for a refund of the money we paid for renting the equipment. Taking into consideration all the trouble we have experienced, I believe we can expect an apology.

I would be most thankful for your support in resolving thisurgent issue.

I look forward to hearing from you.

Yours faithfully,

Steve Adams