AQUA

January:
Balance £1391.16
Interest = 1391.16*0.399/12 = £46.25
Payments £150 (103.75)

Feb:
Balance = 1391.16 - 103.75 = £1287.41
Interest = 1287.41*0.399/12 = £42.80
Payments £50 (7.20)

Mar:
Balance = 1287.41 - 7.20 = £1280.21
Interest = 1280.21*0.399/12 = £42.56
Payments £50 (7.44)

Apr
Balance = 1280.21 - 7.44 = £1272.77
Interest = 1272.77*0.399/12 = £42.31
Payments £150 (107.69)

May:
Balance = 1272.77 - 107.69 = £1165.08
Interest = 1165.08*0.399/12 = £38.74
Payments £75 (36.26)

Jun:
Balance = 1165.08 - 36.26 = £1128.82
Interest = 1128.82*0.399/12 = £37.53
Payments £75 (37.47)

Jul:
Balance = 1128.82 - 37.47 = £1091.35
Interest = 1091.35*0.399/12 = £36.29
Payments £75 (38.71)

Aug:
Balance = 1091.35 - 38.71 = £1052.64
Interest = 1052.64*0.399/12 = £35.00
Payments £75 (40)

Sep:
Balance = 1052.64 - 40 = £1012.64
Interest =  1012.64*0.399/12 = £33.67
Payments £600 (566.33)

Oct:
Balance = 1012.64 - 566.33 = £446.31
Interest = 446.31*0.399/12 = £14.84
Payments £250 (235.16)

Nov:
Balance = 446.31 - 235.16 = £211.15
Interest = 211.15*0.399/12 = £7.02
Payments £218.17 - 100% clear!