Well, its a bit more complex than that unfortunately.
1. You need to find what was the cancellation policy. For avios hotel only bookings the one below is the normal, the £ amount of course changes
Cancellations made less than 3 days before Travel: No Refunds permitted.

Cancellations made more than 3 days before travel: Cancellations made on or after 10/07/22 will be subject to a supplier fee of 175.52 GBP+ £35administration fee. Your original payment in Avios, will be fully refunded to you upon receipt of payment of the above fees.

So you can see that there is a supplier fee for these type of bookings which can be quite high. The contact number you need to call is

Avios Support : 0344 493 0747

However, you have to do the math if you know what was the supplier fee and how much avios you paid for the bookings, ie: is it worth it to fight to get back the avios and pay let say £200 for it?
This is one of the main reason I would discourage anyone to use avios to book any hotels. Usually its better to buy the hotel points (especially we are talking a single night) and use the hotel own currency to book a room. Of course depending on availability so probably you wouldn't able to do that but still using avios to buy anything other than flights, most of the time bad value.
If you decide to fight for it, then you need to raise a claim and customer relation should be in touch in the next couple of weeks.