Don't worry too much. Keep a good record of everything (including phone calls, letters and photos / video of the fault) and do not remove the seal. The last thing you want is to be blamed for tampering. They should be able to book someone in to check/replace the meter. Did they give you a date? If they won't help there is information on the
Ofgem website about the next steps to take. Do not ignore the problem, even if your supplier tells you to, as when they do finally go to read the meter and see it is faulty, it can cause all sorts of issues and arguments over what the bill is, especially if the last reading was months ago. I've seen it happen before.