1999 Fiat Punto Guarntee

Engine Mechanical problem
1999 Fiat Punto Front Wheel Drive Manual 61.000 miles

hello,
i have recently had £900 in repairs on my car which I have owned for 3 months and 2 days ago I was driving home and the engine cut out on me I tried restarting it and couldnt- I was told my cambelt had snapped which is one of the things I have just had replaced, so I have taken it back to the mechanic who repaired it thinking it would be under guarntee and thy have advised the water pump has siezed causing the cambelt to snap and turn into the wool and the mechanic has advised it is not covered under the guarantee and I will have to pay direct as the water pump has siezed and caused the cambelt to snap is this correct? And becuase the cambelt has been replaced should the water pump have been replaced or checked at least?