Problem with noise

Tax Planning and Financial

I received a telephone call at 12.50am (Saturday night) on my mobile, I hurried downstairs after being woken up by the call but just missed the caller but this (approximation) message was left:

"This is Emma ******* (discretion) you have rented your flat out to some people who are drunk and playing music loudly and making a noise in the hallway, I don't know how long I can stand it if it continues I will call the police the council and anyone else I can get involved. If you receive this message in the next 10 mins call them and tell them to be stop"

Although I considered it I did not call the tenants for a combined number of reasons, which were:

1. I could not find their landline telephone number (obviously I will correct that now and keep it in an obvious place) which would have meant ringing a mobile number, but there was no guarantee that the mobile I rang would have been one of the of the 'noise makers'. If I rang anyone it would have been the tenant who I know best who has been there 13 months but for all I knew, he could have been somewhere else asleep and his 2 flat mates may have been responsible for the noise

2. It was 12.50am and I had just been woken from a deep sleep and was far from my best and was thinking that surely the best way for this situation to be handled would be for her to simply knock on the door and ask them to be a bit quieter (which would be what most people would do, she only knows my mobile number because all 4 flat owners in the block own the freehold and therefore have a relationship). After all she was awoken and annoyed herself (understandably so, I do have sympathy for her predicament) but decided to do the same to me without even raising the issue with them, after all it is only a block of 4 flats (not a large dangerous council estate) and they are professionals and appear to be normal, decent, responsible and approachable individuals.

3. When I lived there (about 20 months ago) there was a history of noise from the adjacent flat to me, for all I know it could have been them making the noise and if so I would have possibly woken up my tenants for no reason.

The flat is rented out with the RLA 2006 contract so does obviously have a clause in it about noise/disturbing neighbours.

My query is what should I do, what are my responsibilities as a landlord? Should I send them a letter simply stating I received a complaint? Should I have done anything different at the time (not important now but may be if this ever happens again) i.e. rang one of the tenants up on their mobile (possibly sent a text, but to be honest I did not think of that at the time)? I am trying to establish the best way forward to deal with this in a professional manner treating everyone with the respect that they deserve and also to learn if I should have done anything different at the time.