I suspect, as did Charles, that the breaking treble strings are too long for the intended note. So if you cannot get a refund the easiest solution would be to just drop the range a step or two and get new strings. Sally could probably do the analysis for you or you could contact a professional string maker. Here in the US I use Vermont Strings or Markwood Strings.
As for the levers – since you are new to the harp you probably won’t really need them for a while; just remove the shoddy ones play in the key to which you tune (typically Cmaj in most beginner books). There are decent levers ranging from about $5 US up to really good ones at about $16 each; you can add as many as you want later. A frequent choice is Cs and Fs.
Most people get a harp with levers on every string but that’s not really necessary, it’s just what many makers provide. Frankly I would just leave them off for the time being, learn proper technique, and plan on getting a better harp later. Sally has probably told you about the Musicmakers kits – they are easy to put together -I like the Voyageur model very much – if economy is an issue.